Bishop Fikremariam Hagos "has been released," said Massimiliano Tubani, head of the NGO Aiuto alla Chiesa che Soffre (Aid to the Church Which Suffers), which supports persecuted Christians.
Religious news agency Fides reported in October that Hagos, bishop of Segheneity, was being held in Adi Abeto prison near Asmara after being arrested at the airport on his return from Europe.
He was being held along with two priests: Mehretab Estefanos and Abbot Abraham. Tubani said Estefanos has been released. There was no news on Abraham.
The Catholic News Agency said the trio had been accused of highlighting violations of human rights in Eritrea in their homilies.
Eritrea is one of the world's most closed nations with one of its most authoritarian governments.