Smart materials are being applied more and more widely in semi-active vibration reduction systems. Actuators built with their use are characterized by nonlinearities and hysteretic effects. Their omission in mathematical descriptions may lead to deterioration of the vibration reduction systems. For that reason, it is important to take into account these negative phenomena associated with the actuators at the controller synthesis stage. One method for determining the control laws in semi-active vibration reduction systems that is frequently discussed in academic literature is “Clipped-LQR”. The present paper proposes modification of that method to allow inclusion in the controller synthesis of the hysteretic properties and other nonlinearities of an actuator. The method developed was verified by determining the controller for the semi-active suspension of a machine operator’s seat. A magnetorheological damper was used as an actuator. The dynamic properties of the foam covering of the operator’s seat were included in model. Simulation tests were performed on the vibration reduction system and function of vibration transmissibility was determined. The semi-active vibration reduction system tested was compared to a passive system. The considerations presented herein relate to the semi-active suspension of a machine operator’s seat, and the method presented may be applied to other controlled systems with many degrees of freedom.