According to a judicial source, cleric Ahmed al-Majed and a second defendant were jailed for 15 years, while a third defendant was sentenced to 10 years in prison.
The three were the only defendants to appear in court, as the other six remain at large and were sentenced in absentia to 10 years, the source said.
The first two were allegedly convicted of "forming an illegal group that aimed to jeopardize the (al-Khalifa regime) rule of law and obstruct state institutions from performing their duties,”“ the source said, quoting the list of charges.
The other seven activists were accused of joining the group.
Scores of Shiite activists have faced jail terms over accusations of involvement in violence since protests against the regime of the ruling Al-Khalifa erupted in February 2011.
Despite a heavy-handed crackdown by security forces in mid-March 2011, supported by Saudi-led troops, protesters were largely back in the streets, mainly in Shiite villages.
Dozens of people have been killed in the crackdown, and the security forces have arrested hundreds, including doctors and nurses accused of treating injured revolutionaries.
Bahrainis say they will continue holding demonstrations until their demand for the establishment of a democratically elected government is met.