An electric brake booster for an autonomous vehicle is provided. The electric brake booster includes a body part that receives a power cylinder generating braking pressure in an autonomous driving/braking mode and a master cylinder generating braking pressure in a manual driver braking mode. A driving shaft is movable in an axial direction in the power cylinder and coupled to a piston. A first motor is connected to a first side of the driving shaft and provides driving power thereto. A second motor is connected to a second side of the driving shaft and provides driving power thereto in a direction equal to that of the driving power provided from the first motor. A controller determines whether the first or second motor normally operates and simultaneously or separately operates the first and second motors based on a magnitude of the pressure in the power cylinder or whether emergency braking occurs.