The former science, research, and technology minister said hopelessness and frustration among Iran's youth, which has led to a widespread "brain drain," made him unable to say no.
Moin, who is also a pediatrician, resigned from President Mohammad Khatami's government in July 2003 to protest the mass arrests of students by the conservative judiciary. Moin is backed in the race by Iran's main reformist party, the Islamic Iran Participation Front (IIPF).
Radio Farda correspondent Siavash Ardalan said that by choosing Moin, the reformists are trying to avoid a split in their camp. "Apparently, he was the one that they could achieve consensus on, as much as possible. The reformist groups are trying to avoid candidates that might split the pro-reform camp, and Mustafa Moin seemed to be the candidate that could bring all these reformist groups under one banner. However, two of the main pro-reform groups within this coalition have lent their support to Moin officially. The other ones are yet deciding on whether they want to go ahead with the candidacy of Moin or to choose someone else," Ardalan said.
The former speaker of parliament, Mehdi Karrubi, is being promoted as another possible candidate for the reformists.
It is not clear whether Moin's candidacy will be accepted by the Guardians Council. The hard-line body, which oversees elections in Iran, has the right to veto candidates it deems un-Islamic. The Guardians Council disqualified hundreds of pro-reform candidates during parliamentary elections last February.
Hadi Kahalzadeh, a Tehran-based analyst, said he believes it is likely the Guardians Council will not allow Moin to run. "Our country is unpredictable, but if the current [political] trend continues -- which has intensified after the city-council elections -- it seems that there will be a tendency to reject his candidacy," Kahalzadeh said.
The head of the IIPF, Mohammad Reza Khatami, has been quoted as saying he sees no reason why Moin should be disqualified. Khatami, the brother of the Iranian president, was among the candidates barred from the February elections.
The presidency remains the last stronghold of Iran's reformists. But some analysts say the reformists have little chance of retaining the presidency, pointing to voter apathy and public disillusionment with the reform movement.
Earlier this month, during a speech at Tehran University, President Khatami was harshly criticized by hundreds of students, who accused him of lacking the courage to deliver promised democratic reforms.
Student activists say they have paid a heavy price for supporting the reform movement. Many have been summoned to court, arrested, and imprisoned. Hard-liners control most of the Islamic Republic's key bodies, such as the judiciary and the armed forces, while conservatives gained control over parliament after the February elections.
Several conservative candidates have already announced their intentions to run. They include former Foreign Minister Ali Akbar Velayati, who is now an adviser to Iran's Supreme Leader Ayatollah Ali Khamenei, as well as Mohsen Rezai, the former Islamic Revolution Guards Corps commander who is now secretary of the powerful Expediency Council.
The former head of Iranian state television and radio, Ali Larijani, who represents Khamenei on the Supreme National Security Council, may also enter the race. Iran's influential former President Ali Akbar Hashemi-Rafsanjani -- who is considered to be a pragmatic figure on the political scene -- is also considering an election bid.
As Radio Farda's Ardalan noted, Rafsanjani uniquely enjoys support from both the reformist and conservative camps. "Their support is really stemming from their own factional interests, as the reformist groups feel that, even though if they had differences with Rafsanjani in the past, that his presidency could stem the efforts of the hard-liners to take Iran in a different direction," Ardalan said. "And also, the hard-line groups, as much as they would not like to see Rafsanjani become president, nevertheless, they feel that if he decides to announce his candidacy and officially enters the election scene, that might take away votes from the other official conservative candidates so they would have no choice but to support him. That's why they are playing a waiting game."
The exact date of the election has not been announced, although it is expected to be held in May or June.
Earlier this month, Iran's interior minister criticized the Guardians Council for proposing to push back the presidential election. The state-run news agency IRNA quoted Abdolvahed Musavi-Lari as saying the council has no jurisdiction over the timing of elections.
(Radio Farda's Keyvan Hosseini contributed to this report.)