Drewery Dyke of the London-based rights group says Mohammad Mostafaei is expected to travel to Norway in the coming days.
Mostafaei maintained a blog that sparked a worldwide campaign to free his client, Sakineh Mohammadi Ashtiani, who was convicted of cheating on her husband.
He fled to Turkey after being questioned then released in Tehran. He was detained because of an undisclosed passport problem.
The U.N. refugee agency confirmed his release, but would not provide further details.
Tehran says it will not carry out the stoning against Ashtiani for the time being, but the mother of two could still face execution by hanging.