He died during the filming of "The Game of Death." His death was not related to the filming. His character died in The Chinese Connection (Jing Wu men).
Bruce Lee died from cerebral edema, caused by an abnormal reaction from painkillers Lee took to treat a headache. Brandon Lee, his son, died in the making of The Crow by a fired prop gun.
The cause of Bruce lee's death is unknown. Some people say monks killed him and some say that he had cerebral edema. So the answer is unknown but it might be one of these causes.