A Shia man was shot dead late on Friday in the fractious Qatif district of Saudi Arabia's Eastern Province, home to many of its Shia Muslim minority.
The shooting brings to 19 the death toll since early 2011 during protests by Shias demanding equal rights with the Sunni majority, and in clashes with police in the towns and villages around Qatif.
Shia activists said the 19-year-old Shia was shot in his car by a stray bullet fired by police when they fired at another person on a motorbike.
An Eastern Province police spokesman said in a statement carried on state media he was shot when they exchanged fire with unknown gunmen, adding he was found in his car at dawn on Saturday but was dead before reaching hospital.
The shooting happened at around midnight on Friday, he said.
Saudi Arabian Shia complain of entrenched discrimination in the birthplace of Islam, which follows the rigid Wahhabi Sunni school that views the minority sect as heretical.
The Saudi authorities deny charges of discrimination and have said each of those killed since protests began in early 2011 were shot in exchanges of fire. Shia activists have said some were unarmed protesters shot during peaceful rallies.
Protests and shootings in Qatif have mostly focused on the village of Awamiyah and spiked last summer after the arrest of a prominent cleric.
Saudi authorities have accused Shia Iran of being behind some of the unrest in the area, a charge denied by both Tehran and local activists.