A Saudi court in Eastern Province on Wednesday sentenced two Shiites to prison terms over riots in the predominantly Shiite district of Qatif, a judicial source said.
The sentences were among verdicts issued by the court in the case of five men accused of rioting.
One defendant was sentenced to four months, but his release was ordered as he has already spent that long in custody, the source said, requesting anonymity.
The court jailed another to two months after he had been out on bail, the cases of two others were adjourned until Sunday, and a fifth was acquitted for lack of evidence, the source said.
"The prosecution protested the sentences and demanded they be toughened," he added.
Those sentenced admitted taking part in protests and signed a pledge not to do so in future, the source said.
On Saturday, the court began the trials of an unspecified number of Shiites accused of taking part in illegal rallies and chanting anti-government slogans.
Since early 2011, mainly Shiite towns in Eastern Province have seen sporadic protests and confrontations between police and Shiites who claim they have been marginalised.
There are an estimated two million Shiites in the Sunni-dominated kingdom.
The unrest erupted after violence between Shiite pilgrims and religious police in the Muslim holy city of Medina in February 2011.
The protests escalated when the kingdom led a force of Gulf troops into neighbouring Bahrain the following month to help crush Shiite-led pro-democracy protests in the Sunni-ruled kingdom.