Dr Sa’ad al-Faqeeh, of the Islamic Reform Movement, was speaking after at least six members of an armed opposition group and two Saudi policeman were killed in a gun-battle in the northern region of Qasim.
Speaking to Aljazeera from London, al-Faqeeh said the six "were either seeking protection in the area or were preparing for an operation in the al-Fuwailiq US military base, which was used by the US forces during the war on Iraq".
Al-Faqeeh said seven members of the security forces were killed in the clash, which occurred in an area which heavily supports the opposition Jihadi movement.
High-profile dissident dead
He added that a high-profile wanted Jihadi member called "Al-Dakheel" was among the dead.
June 18, 2002 - seven suspected members of al-Qaida captured
Feb 18 - 90 Saudi nationals put on trial for belonging to al-Qaida
May 12 - 35 people killed and 200 others wounded in suicide bombings in Riyadh
May 19 - Three Moroccans arrested for "planning to crash an airliner in Jeddah"
June 14 - Five "terror suspects" killed in Mecca
Sources say that security forces got the information about the group's whereabouts from a tip-off.
They then besieged the suspects, who were hiding out on a farm, using a large deployment including policemen and special security forces.
According to Saudi officials, at least eight officers were injured in the shootout, but they would not confirm any deaths.
One suspect was recovered alive, an unidentified interior ministry spokesman added.
Saudi Arabia is cracking down on armed opposition group members who see the government as a legitimate target because of its close relationship to the United States.
A suicide attack on a housing compound left 34 people, mostly westerners, dead in May.