Hossein Derakhshan, nicknamed the "Blogfather" for his role in pioneering a blogging revolution in Iran, last updated his blog in October and Canadian media reports, quoting a friend, said he was detained on November 1 during a visit to Iran.
Derakhshan was being held on charges of spying for Israel, a country the Islamic republic does not recognize, according to Canadian media.
"His case is in a preliminary investigative stage at a revolutionary court and he is currently in incarceration in a jail in Tehran," judiciary spokesman Alireza Jamshidi told a news conference when asked about Derakhshan's case.
Revolutionary courts handle national security cases.
The spokesman did not give further details.
Iranian Nobel Peace Prize winner and rights lawyer, Shirin Ebadi, earlier in December called for Derakhshan's release, although at the time she said she could not confirm independently that he had been detained.
Derakhshan, 33, was a journalist in Tehran before moving to Toronto in 2000. He made his name by publishing instructions on how to use blogging software to publish blogs in Farsi, sparking an explosion of blogging in the Iranian language.
Critical of the Tehran government in the past, Derakhshan has recently been more sympathetic to Tehran. He visited Israel in 2006 and said at the time that this might mean he would not be able to go back to Iran "for a long time."