Hassan Heidari, deputy prosecutor general of Khorasan Razavi province in northeast Iran, said the 11 defendants, including women, were also convicted of "propaganda against the system of the Islamic republic".
Several of them were found guilty of having set fire to two mosques in the city of Masshad, IRNA said, adding that the rulings were subject to appeal.
Attacks on mosques, worshippers soar in Afghanistan: UN
According to Iranian authorities, the accused form part of an opposition group called "Restart" which was established by Mohammad Hosseini, a onetime game show host on state television who has gone into exile.
He is alleged to have called on social media for Iranians to attack mosques, banks and centres run by the Basij, a hardline militia linked to the Revolutionary Guards.
In October, several banks in relatively affluent northern Tehran were targeted in nighttime attacks.
At least 25 people were killed in a wave of social unrest that swept towns and cities across Iran between December 28 and January 1.
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