(Why am I posting this?)
Ganji was near the end of a six-year sentence
Akbar Ganji's family told the BBC that police came to the family house to arrest him on Tuesday night but he was not home and he has not returned since.
The authorities are quoted as saying he has gone on the run, but his wife believes he may have been arrested.
Human rights groups say Mr Ganji is a political prisoner, and want him freed.
He was jailed in 2001 after being convicted of charges including lying and endangering state security.
Mr Ganji, who was near the end of his six-year sentence, was granted leave from prison last month for a series of health tests.
The semi-official news agency Fars said a warrant was issued for his arrest after he failed to present himself to authorities when his leave expired.
Tehran's chief prosecutor, Saeed Mortazavi, told Fars: "Bailiffs went to Ganji's house with the arrest warrant, but he was not home and he has still not returned and has gone into hiding."
Mr Ganji's wife, Massoumeh Shafii, told Reuters news agency her husband had gone to a friend's house but had not come back.
"I don't know if he was arrested or where he is. We're very worried."
She was quoted as saying authorities ordered her husband detained because of a series of media interviews he gave last month.
Mr Ganji's trial and imprisonment was part of a wider struggle between Iran's reformist movement, lead by President Mohammed Khatami, and conservative clerics and judiciary.
Dozens of reformist journalists, politicians and intellectuals have been jailed in recent years.
Human rights group Amnesty International regards Mr Ganji as a political prisoner and has long called for his release.