Downing Street said Jonathan Evans' briefing was 'routine' and not prompted by any new threat or intelligence, and Home Secretary Teresa May also addressed the group on legislative efforts to fight the terror threat.
But with the main Olympic Park in Stratford protected by an unprecedented security operation, including the possibility employing surface to air missiles to combat any threat from the sky, it may be that any planed attack could be launched at one of the other, out-of-town, Olympic venues.
Eton Dorney, 25 miles to the west of London, will host rowing events, cycling will go out into the Surrey countryside, sailing is taking place off Weymouth and football is being played in Newcastle, Coventry, Cardiff, and Manchester.
The police and armed forces have been working on Olympic security plans since London won the right to host the Games seven years ago, with Royal Marines having staged training exercises on the River Thames and air and water-borne security officers practicing tackling boats.
Mr Evans is a regular member of discussions involving the Prime Minister's National Security Council, which includes senior ministers, security chiefs and top military officials, and a spokesman said the PM was 'keen that some of those discussions that would generally happen at the NSC are occasionally brought to the full Cabinet.'