The case, which began in February 2017 with the arrest of eight individuals, gained attention following the death of Kavos Seyyed Emami while in custody.
Sentences ranging from four to ten years were initially handed down, but recent announcements of amnesty have led to the release of the remaining activists.
They were charged with espionage and collaboration with the hostile government of the United States.
Morad Tahbaz was released last year in an exchange, while Abdolreza Kohpayeh and Sam Rajabi completed their sentences earlier.
In the latest development, Nilofar Bayani, Homan Jokar, Taher Qadirian, and Sepideh Kashani have been freed, with their remaining sentences forgiven.
