The object - believed to be a camera - caused the game to be stopped after it had appeared to be thrown towards Chelsea midfielder Frank Lampard.
The referee, Andre Marriner, mentioned the incident in his match report and the FA will now contact the Gunners as they gather further information.
However, because the object did not strike any player or official, the likelihood of severe sanctions against the club are minimal.
Chelsea cruised to a 3-0 victory in the derby thanks to a brace by Didier Drobga and a Thomas Vermaelen own goal.
Source: DSG