This paper considers the prescribed performance control of unknown multi-input multi-output nonlinear systems with actuator faults. By combining a special funnel function and a barrier function, based on a new coordinate transformation, a low-complexity control approach is proposed not only to guarantee the full-state errors converge into a desired steady-state error boundary in a predefined time, but also to tolerate time-varying actuator faults and achieve the asymptotic tracking, as opposed to the semi-global bounded error tracking results. Our design has a simple structure in the sense that repeatedly taking derivatives of virtual controllers is avoided, and by introducing a time-varying function for the gain design, function approximation methods are also unnecessary. It is applied to the two-degree-of-freedom helicopter system, which demonstrates a good performance in the transient and steady-state stages.