In a typical approach to model electrical stimulation of an axon, a cable model equivalent to an axon was placed in a simple homogeneous medium. An electrode was used to induce an excitation to stimulate the cable model, and then the transmembrane potentials and the ionic currents in the cable model in temporal domain were observed. Unfortunately, this simulation approach is not realistic since inhomogeneous tissues near the axon is not considered. In this paper, the alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is coupled with the equivalent model of a membrane (the Hodgkin-Huxley model), and a novel simulation scheme is developed to predict axon activation. By testing axon activation with current excitation, the simulation results show the new method is useful for simulating axon activation.