The 20 people were charged under Ethiopia’s controversial anti-terrorism law and convicted last month.
All but one received prison terms of five and a half years. Two were journalists working for a Muslim radio station.
Muslims have reportedly felt marginalized in Ethiopia for long, and have occasionally held protests since 2011.
The state-affiliated Fana Broadcasting Corporate, citing the court ruling, said Tuesday that the 20 defendants also were found to be “participating in a movement to secure the release of another Muslim group that was under detention.”
The Ethiopian government in October declared a six-month state of emergency in the face of an unprecedented wave of violent protests that begun in the Oromia region before spreading to other parts of the country.