In this paper, we propose a design scheme of an adaptive PID tracking control system for discrete-time nonlinear SISO systems. The proposed method utilizes the output feedback strictly passive (OFSP) properties of the controlled system, so that the stability of the resulting adaptive control system can be guaranteed with certainty. A robust adaptive PID design scheme for the OFSP augmented system with a parallel feedforward compensator without causality problems was developed by introducing an adaptive neural network (NN) feedforward control signal.