An active vibration suppressor for suppressing vibrations in structures, such as buildings, has an actuator attached to the structure and an extendable rod of the actuator attached to a seismic mass which is thus moved by the actuator. A sensor is attached to the structure adjacent to the actuator and connected to a compensated power amplifier which operates the actuator. Movement of the structure is sensed and the actuator moves the seismic mass in a direction to oppose the structural displacement thereby minimizing structural vibrations.