Zuhair al-Said and Munir al-Medani
Saudi security forces killed two protesters when they opened fire on a march in the oil-producing Eastern Province, home to a large Shia minority.
Zuhair al-Said, 21, was killed as security forces dispersed a protest on Friday against the death of another Shiite demonstrator the previous day, activists said.
"Eight armoured vehicles belonging to Saudi security forces intervened to disperse the protest," the activist said.
Munir al-Medani, also 21, died of his wounds on Thursday after being shot by security forces in the Al-Shwaika neighbourhood of Qatif during a demonstration for reform activists said.
Demonstrators also took to the streets of another Qatif town -- Al-Rabieya -- on Friday to protest against Medani's death, activists said.
"Hundreds of demonstrators waved pictures of those killed and detained as they condemned the shooting (by Saudi security forces) on peaceful protests," one activist told AFP.
Activists and witnesses said that Medani's death came when security forces opened fire on a Shiite procession marking the birthday of the Prophet Mohammed -- a celebration forbidden in Saudi Arabia -- which turned into a demonstration for reform and the release of Shiite detainees.
Zuhair's death raises to seven the number of protesters killed since demonstrations erupted in the Eastern Province last March.
Activists say that Saudi authorities have arrested nearly 500 people since the protests started. Many have been released but dozens remain in custody, among them human rights activist Fadel al-Munasif and writer Nazir al-Majid.
In January, Saudi authorities published a list of 23 men wanted on suspicion of involvement in the disturbances.
Later the same month, the interior ministry announced that security forces had arrested nine people suspected of involvement in the wounding of three policemen in the Eastern Province.
Most of Saudi Arabia's estimated two million Shiites live in the province, where the vast majority of the kingdom's huge oil reserves lie. They complain of marginalisation in the Sunni-dominated kingdom.