Hessam Firuzi's wife, Mahtab Bordbar, told Radio Farda her husband was released from Tehran's Evin prison on October 4 after holding him for one day.
Bordbar said the reasons for the arrest of her husband, who had earlier urged Iranian authorities to free jailed student activist Ahmad Batebi on health grounds, were unclear.
"[Authorities] told him he should deny Batebi's health problems and also say that [late student leader] Akbar Mohammadi was ill," she said. "He did not accept. They eventually told him he could go."
The 36-year-old Mohammadi died at Evin prison on July 30 under unclear circumstances. International rights groups have urged Iranian authorities to investigate his death.