They were detained as part of a group of five, and two more remain in prison.
The group; Mohammad Dehnavi, Hadi Asgari, Amin Afshar Naderi, Ramil Bet-Tamraz and Amir Dashti, were arrested during a trip to the Alborz Mountains north-east of Tehran in August.
Mr Bet-Tamraz, Mr Dehnavi and Mr Naderi were then released after posting bail of around £28,000 ($33,000 each), according to Middle East Concern.
The men are not clear what charges they have been arrested on, and Middle East Concern said they were asked questions in relations to one of the men's fathers who is a pastor during their interrogation.
Ramil Bet-Tamraz's father, Victor, is a Christian leader who is still awaiting a court summons over his arrest, alongside his son, on Boxing Day 2014.
The two remaining jailed men are reported to have faced "intense pressure" during their interrogation.
It is not clear if or when they will be released.
