By using a CMOS compatible process technology, a MEMS variable optical attenuator (VOA) is characterized in terms of actuation mechanisms. A dual-fiber collimator is aligned perpendicularly to the micromirror in a three-dimensional (3D) free space configuration, where the micromirror is mechanically connected with an electromagnetic actuator and two sets of electrothermal actuators. Three types of attenuation schemes based on electromagnetic, electrothermal and hybrid, i.e. combination of electrothermal and electromagnetic, actuations have been explored and studied. Dynamic attenuation ranges of 40 dB have been achieved at 4 Vdc, 26 mW and 3 Vdc, 20 mW by electromagnetic and electrothermal attenuation schemes respectively. Wavelength-dependent loss has been demonstrated to be less than 0.6 dB at all attenuation states for both attenuation schemes. In the hybrid attenuation scheme, various voltage combinations are made to the electromagnetic and electrothermal actuators. An optical attenuation of approximately 40 dB can be obtained when two volts are applied to both the electromagnetic and electrothermal actuators simultaneously, while the electrical power consumption of the actuators is 17 mW in total. Our unique design of using both electrothermal and electromagnetic actuators simultaneously to achieve attenuation is the first demonstration of such a hybrid-driven CMOS compatible MEMS VOA device.