The Iranian daily Shargh reported on Sunday that Akbar Ganji was being given seven days of leave.
Ganji was jailed in 2000 after he alleged top government officials were behind the murders of dissidents.
Ahmad Batebi, Nasir Zarafshan and Akbar Muhammadi were each given five days out of prison.
Batebi had been initially condemned to death for his participation in a demonstration in 1999 where he was featured on a famous photograph holding aloft a blood-soaked T-shirt.
His sentence was revised to 13 years imprisonment.
In August 2002, Zarafshan, a prominent lawyer was sentenced to five years in prison and 50 lashes for "distributing secret information".
He was the legal representative of the Forouhar and Pouyandeh families, three of whose members were killed in a series of murders officially attributed to "rogue" intelligence ministry agents in November 1998.
Popular public demonstrations
appear to be having effect
Akbar Muhammadi was originally sentenced to death for "warring against God" for his role in the 1999 student demonstrations, and is currently serving a reduced term of 15 years.
Statement of rights
Reza Alijani, Huda Saber and Taghi Rahmani, who are members of Iran's liberal opposition, were also given a week's leave.
They were imprisoned on charges of seeking to topple the Islamic republic's government.
The measures were announced a few days after judiciary head Ayat Allah Mahmud Hashimi Shahroudi, published a series of directives to strengthen the rights of the detainees, including banning torture during interrogation.
Shahroudi stressed the principle of presumption of innocence and respect for legality, the right of detainees to have a lawyer and condemned abuse of power and improper imprisonment.
The moves also come amid the resurfacing of debate on whether there are political prisoners in Iran or not.