Rotor unbalance in an AMB-based gyroscopic sensor is studied in this paper. An AMB-based gyroscopic sensor has been proposed to realize a high-accuracy, low-cost and compact gyroscopic sensor. In this sensor, an active magnetic bearing (AMB) is applied as a rotating gyro, which is an instrument for measuring angular velocity. The relative position and attitude of the AMB rotor to the AMB stator are maintained using magnetic forces. Two-axis angular velocities of a measurement object are estimated from the control currents required to cancel the gyroscopic torque acting on the AMB rotor. However, the estimated signals of angular velocities include several undesirable frequency components. These components are caused by rotor unbalance and the induction motor used to spin the AMB rotor. A beat appears due to composition of these components. The beat component cannot be eliminated by filtering because it is in the measurement bandwidth of the AMB-based gyroscopic sensor. In this study, two unbalance compensation methods are applied to the AMB-based gyroscopic sensor to eliminate the beat component from the estimated measurements of angular velocities. The efficacy of each compensation method is examined experimentally.