All 16 are members of the outlawed Oromo Liberation Front. They received sentences of four to 13 years.
The Ethiopian Federal High Court said in its ruling on Tuesday the members tried to carry out terrorist acts across the country and supported other group members in remote parts of Oromia.
The region has been a hotspot for anti-government protests that began in November 2015. The protests later spread across the country and demanded wider political freedoms and the release of political prisoners.
The protests led to the killings of hundreds of people and the declaration of a nationwide state of emergency that remains in effect.