RNA - Abdulaziz al-Shubaily will also be barred from writing on social media for eight years after his release and will not be allowed to travel, the (Persian) Gulf Center for Human Rights said in a statement, the Daily Star reported.
The verdict "is essentially the same" as one issued against him in May, said the center, which has offices in Copenhagen and Beirut.
It said Shubaily refused to recognize the court because it deals with terrorism offences. An appeals court had sent his case back to the "Specialized Criminal Court" for a further review.
Shubaily has "used social media networks to call for reform and defend people's rights" in the absolute monarchy, the Center said.
Shubaily was a leading member of the Association for Civil and Political Rights, which was dissolved by a Saudi court in 2013.
He was the last of the group's founders to be locked up, London-based Amnesty International has said.
Amnesty has denounced the kingdom's "cynical use of a repressive and overly vague counter-terrorism law" against civil society.
The Center said the ruling against Shubaily, "which was issued after a mock trial that did not follow international standards and due process, is part of an ongoing trend adopted by the authorities".
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