<p>Gears are widely used in high-speed rotating machinery. Their dynamics are affected by their inherent nonlinearities that include gear tooth backlash and time-varying mesh stiffness. Most of the works on geared rotor system in the past considered bearing support with linear stiffness and damping coefficients. In recent years, however, active magnetic bearings (AMBs) have been used to support geared rotor system. The use of AMBs, which are highly non-linear machine elements, can influence the dynamics of geared rotor systems. The present work considers a geared rotor system supported by AMBs. The nonlinearities of the AMBs are due to the relationship between the magnetic force with the air gap and coil current, as well as the geometric coupling between two orthogonal magnetic actuators. Two models of the gear were used in this work. The first model considers a time-varying pressure angle and a dynamic backlash, whereas the second model considers a constant pressure angle and a constant backlash. Numerical simulation was undertaken for a range of design and operating parameters of the geared rotor system supported by AMBs. Numerical results showed that the onset speed of non-periodic vibrations for the time-varying pressure angle and a dynamic backlash model was lower compared to the model with a constant pressure angle and a constant backlash. The influence of the air gap length of the AMB was also determined from the numerical results. Increase of the air gap length was seen to change the response of the geared rotor system from periodic to non-periodic for both models. The present work had shown that the air gap length of the AMBs is a more dominant factor compared to the pressure angle and backlash of the gear, in determining the dynamic response of geared rotor system supported by AMBs.</p>