Active noise equalizer systems are used to adjust the noise level in an environment, based on the preference of retaining noise information. Several researches have been carried out to determine the maximum step size bond of narrowband active noise control system with perfect secondary path estimation without gain factor consideration. However, in practical environment, secondary path estimation error of the system exists. In this paper, a stochastic approach analysis is applied to determine the maximum step size of the system under imperfect secondary path estimation. Simulation results are conducted to verify the analysis. Results show that the gain factor, sampling frequency, and secondary path estimation errors are all major factors governing the maximum step size of the narrowband active noise equalizer system under imperfect secondary path estimation.