In order to improve the healthcare services quality, various initiatives have been carried out to develop new assistive technologies such as wearable robots. This paper deals with the control of an actuated knee joint orthosis dedicated to assistive and rehabilitation purposes. The proposed control scheme is based on a nonlinear state feedback complied with a linear quadratic regulator (LQR) in a cascaded control architecture. The proposed control scheme has been validated in simulation for the control of an active orthosis in various operating conditions and compared with a PID controller. The obtained simulation results show clearly the efficiency of the proposed control scheme and its superiority with respect to the PID in terms of the tracking performance and the comfort of the user.