In a conventional narrowband active noise control system, each narrowband component is cancelled separately, but each control coefficient is still updated by the overall residual error of the system. This leads to the interferences among the controllers, thus reducing the convergence rate of the system. In order to ensure that each controller uses its own residual error to update the control coefficient and to separate frequency components from residual error signals, a complete narrowband active noise control system based on leaky residual error separator is proposed, and the corresponding preliminary statistical analysis on the new system is derived. Extensive simulations and experimental results as well as theoretical analysis demonstrate that the robustness and convergence performances can be improved without increasing the residual noise in the steady state by using the residual error separator that introduces the leakage factor.