The 37-year-old hip-hop artist, whose stage name - Adjoguening - meaning "warrior sage," was arrested on September 13 in the capital Malabo while staging a protest over the confiscation of his passport, his lawyer, Andres Nsue Ntutumu, said.
He had been carrying a sign around his neck reading "Give me my passport back," the attorney said, adding that the authorities had provided no information about any charges against his client since his release on Wednesday.
"He outwardly seems to be well, but this has to be confirmed by medical tests," his brother said.
The small oil-rich central African nation is one of the most authoritarian and enclosed states in the world.
Its iron-fisted ruler, President Teodoro Obiang Nguema Mbasogo, has been in power for more than 43 years -- the longest tenure of any living head of state today except for monarchs.
The security forces have been carrying out a wave of detentions among artists and dissidents since mid-September ahead of presidential and legislative elections on November 20, rights monitors say.