Faisal Hayyat, a journalist and a blogger who hosts a satirical channel on YouTube, was convicted yesterday of insulting a "religious symbol and group," the watchdog said.
He has been in detention since October 9, the last time he tweeted saying that he had been summoned by police for investigation.
The content of the tweet that the charges refer to is not clear, but on October 8, Hayyat posted tweets denouncing Muawiyah, the first caliph of the 7th-century Umayyad Caliphate, who is despised by Shiite Muslims for a conflict with their revered Imam Ali.
Scores of Shiites have been jailed on charges of involvement in the unrest and others have been stripped of their citizenship.
The crackdown has drawn criticism from the United Nations and the United States.