The Bahraini High Court of Appeal also convicted six of the defendants of establishing contacts with a foreign country to carry out hostile attacks, Bahrain News Agency reported Tuesday.
Seven of the defendants will serve life sentences while the rest received prison terms ranging from five years to 15 years.
Among those convicted was Abdulhadi al-Khawaja who went on a 110-day hunger strike to protest his detention, the BBC reported.
Bahrain has been wracked by unrest since demonstrators occupied a prominent landmark in Manama in February 2011.
They demanded more democracy and an end to discrimination against the majority Shiite Muslim community by the country's Sunni royal family.