The National Organization for Human Rights said Monday that Karim Antoine Arbaji, a 31-year-old who writes frequently about corruption in the country, was sentenced a day earlier.
NOHR said Arbaji has been repeatedly summoned by the agency over his writings, and was detained in 2007.
NOHR did not specify what prompted his conviction.
The group called on Syria to free its political prisoners.
Since coming to power in 2000, President Bashar Assad has freed political prisoners and passed laws aimed at liberalizing the state-controlled economy. But he has also clamped down on political activists.