Ibrahim al-Sadek al-Kaydi al-Harbi "is on his way to Saudi Arabia" from the Syrian capital, said Fawaz al-Harbi from the holy city of Mecca.
Al-Harbi, 33, who is not on a most-wanted list issued by Saudi authorities, is only the fourth to turn himself in under a one-month amnesty offered by King Fahd on 23 June to Islamist dissidents who surrender.
On Tuesday, Khalid bin Odeh bin Muhammad al-Harbi, alias Abu Sulaiman al-Makki, presumed to be a top al-Qaida figure close to Usama bin Ladin, was flown back to Saudi Arabia after turning himself in to his country's embassy in Iran.
Fawaz al-Harbi, who is director of the religious institute at the Grand Mosque in Mecca, Islam's holiest shrine, said his brother, Ibrahim, phoned another brother a week ago and told him he wanted to give himself up, which the brother encouraged him to do.
Assistant Interior Minister Prince Muhammad bin Nayef ordered that arrangements for his return be speeded up after the Saudi embassy in Damascus failed to deliver promptly, he said.
Al-Harbi fought in Afghanistan during the Soviet invasion of that country in the 1980s and subsequently in Bosnia, where he was wounded, according to his brother.
Security forces expected to
crackdown after amnesty expires
He returned to Saudi Arabia before dropping out of sight in the wake of the September 11 attacks.
But Fawaz al-Harbi said his brother was not a member of bin Ladin's al-Qaida network and had no links with dissident cells blamed for a wave of violence which has killed some 90 people and wounded hundreds since May 2003.
He alleged that his brother was wanted by security authorities to be questioned only about his stint in Afghanistan.
Thirteen dissidents on the most-wanted list remain at large, down from 26 when it was issued last December.
The others have been either killed in clashes with security forces or surrendered, including one who gave himself up under the amnesty offer.
Interior Minister Prince Nayef bin Abd al-Aziz on Monday said there would be no extension of the amnesty despite its poor results so far, although he expressed the hope that more suspects would come forward.
Authorities have repeatedly warned that dissident-suspects will face a harsh crackdown if they do not surrender within the set deadline.