In the first case, the appeals court confirmed 15-year prison sentences against each of 10 defendants convicted of attempting to murder four policemen, the source said.
They targeted the policemen in April 2012 in the Shiite village of Akr, near the capital Manama, according to the charges.
A lawyer said the verdict ignored accusations by the defendants that they had been tortured into giving confessions.
In the second case, the court upheld 10-year jail terms against each of three Shiites convicted of attempting to murder policemen in the village of Karzakan in February last year.
The defendants were accused of opening fire on policemen who were dispersing demonstrators in the village.
The court also upheld jail terms against five defendants in a third case, convicted of forming a "terror group" which prepared a car bomb that police uncovered in the Shiite area of Sitra.
Two defendants have been jailed for 15 years, while the remaining three each received 10-year sentences.
A month-long protest that erupted on February 14, 2011, challenged the regime of the Shiite-majority kingdom that is ruled by the Sunni Al-Khalifa dynasty.
The demonstrations were broken up in mid-March in a deadly crackdown helped by security forces from neighbouring Saudi Arabia.
At least 89 people have been killed in Bahrain since the protests began, according to the International Federation for Human Rights.
Demonstrators frequently clash with security forces in Shiite villages outside the capital.
Bomb attacks have included one that targeted a Sunni mosque close to the royal court last July. It caused no casualties.