The arrests come on the eighth anniversary of an attack by police forces and vigilantes on a university dormitory in Tehran that is regarded by some government critics as a symbol of continuing political repression.
It is unclear where the student detainees were taken after being picked up by authorities this morning. The six members of the pro-reform student groups had staged their protest for about one hour when police forces and plainclothes agents reportedly detained them and took them to an unknown location.
The student group's website, advarNews.com, has identified them as a woman and five men: Bahareh Hedayat, Mohammad Hashemi, Ali Nekunesbati, Mehdi Arabshahi, Hanif Yazdani, and Ali Vafaghi.
Student leader and Abdollah Momeni told Radio Farda earlier today that their families have sought in vain to learn where the detainees are being held.
"There is no news about the location where the members of the central council of the Office to Foster Unity are being detained. Their families and also individuals who are due to represent them are following the issue -- they've gone to the prosecutor's office, but so far there has been no news about their situation or where they're being held."
Shortly after Momeni spoke to RFE/RL, he and a number of other students were also detained following a raid on the student group's office.
The cause of the arrests is unclear, and authorities have so far avoided commenting on today's events.
The six members of the reformist student group's central council had vowed ahead of their arrests to protest the continued imprisonment of eight fellow students.
They had pledged to mark the anniversary of the day eight years ago when plainclothes vigilantes violently attacked a dormitory in Tehran. That attack led to a week of civil unrest and massive arrests that marked an iconic confrontation between government-backed forces and students in Iran's postrevolutionary history.
Students have tried to mark the date each year with protests, but they have met with official curbs.
This year's anniversary comes amid heightened pressure on student activists and universities as part of what is being described by some as a "cultural revolution" by President Mahmud Ahmadinejad's government.
Nekunesbati, one of the student activists who was detained today, told Radio Farda on July 7 that arrests and the summoning to court of students represent an attempt by authorities to prevent commemoration of the student unrest, known as or "18 Tir."
"This is a message to students to refrain from having any protest action on the anniversary of 18 Tir," Nekunesbati said. "The wave of violence against students that we are witnessing in recent days shows that [authorities] want to prevent any ceremony from taking place on that day. Of course, we should not ignore the fact that [authorities] are facing many problems and because of that they have put all their critics under pressure."
Jailed, Not Forgotten
Nekunesbati also expressed concern about the fate of eight students from the Polytechnic University (Amir Kabir) who have been in jail -- and incommunicado -- for around two months.
They include students who had organized an anti-Ahmadinejad protest when he visited their elite university in December. Reports at the time said students held pictures of the Iranian president upside-down, burned several of them, and implied he was a dictator and a fascist.
Some protesters chanted that "students will die, but they will not accept humiliation," and called for "death to the dictator."
Ahmadinejad cited the incident as evidence that Iranians are allowed to protest with total freedom.
But some students suggest the arrests of the polytechnic university students -- including three editors of student publications -- came in retaliation for that protest.
Today's arrests come with at least one of the students who was arrested in Tehran eight years ago still in jail. Several human rights groups have called for the release of Ahmad Batebi, who reportedly suffers from health problems as the result of ill treatment in prison. But authorities have ignored such calls.
(Radio Farda correspondents Farin Assemi and Hamid Fatemi contributed to this report.)