Rasa News Agency reports - The defendant, whose name was not given, was found guilty of taking part in protests in Qatif in Eastern Province and calling for the withdrawal of Saudi forces sent to Bahrain.
Saudis helped Bahraini security forces to crush a Shiite-led uprising demanding democratic reforms in Sunni-ruled but Shiite-majority Bahrain in March 2011.
The defendant was charged with throwing petrol bombs at security forces who intervened to disperse protests in Qatif, Al-Hayat newspaper reported.
It said both the accused and the prosecutor, who had demanded the death penalty, will appeal.
Protests first erupted in Eastern Province, where the majority of the kingdom's two million Shiites are concentrated, in March 2011.
Ten people were killed in a series of clashes with security forces, and the fighting intensified after the arrest in July last year of Sheikh Nimr al-Nimr, considered to be a driving force behind the protests.
However, tensions eased when seven Shiite dignitaries from Qatif hailed a call by King Abdullah for the creation of a centre for Sunni-Shiite interfaith dialogue.