Uthman al-Amri, one of 26 suspects listed in December by Saudi Arabia, gave himself up early on Monday in the southern Asir province, said one of his cousins, who declined to be named.
Saudi Arabia has been battling a wave of violence blamed on suspected al-Qaida fighters. At least 85 police and civilians, many of them foreigners, have been killed in bombings, shootings and kidnappings by dissidents battling to topple the ruling monarchy.
A Saudi security source said al-Amri, who had fought in Afghanistan, was close to Saaban al-Shihri, a dissident who also turned himself in last week. Shihri was not on the list of 26 suspects.
Crown Prince Abd Allah: Suspects
will be treated 'under God's law'
In a televised speech delivered on behalf of King Fahd last week, de facto ruler Crown Prince Abd Allah gave dissidents a final chance to surrender under a limited one-month amnesty and be treated "under God's law".
Officials said the state would drop its claims against those who surrendered, but that it would be up to the relatives of victims to decide whether they should face charges over any attacks they had been involved in.
The offer of a pardon came close on the heels of the 18 June killing of Abd al-Aziz al-Muqrin, described as a local al-Qaida leader. He was accused of the kidnapping and beheading of American Paul Johnson.
Saudi Arabia's chief diplomat has meanwhile sought to assure Westerners that their security is a top priority for officials, in an effort to assure expatriates fearful the spate of attacks is not over.
"We will assume our responsibilities to ensure their safety and security the same as the security and safety of our citizens," said Foreign Minister Prince Saud al-Faisal after meeting Western ambassadors on Sunday.
He underlined that the Saudi government was prepared to allow foreigners to carry guns.