In this paper, we consider the leader-following consensus problem of a group of autonomous agents with discrete-time model. The velocity of the active leader is assumed to be unknown in real time. To track the active leader, a neighbor-based local control law and a neighbor-based state-estimation rule for each autonomous agent was provided. By using the graph theory, matrix theory and Lyapunov function method, some sufficient conditions are established for the consensus stability of the considered systems under fixed topology case and switching topology case respectively. Finally, numerical simulations are given to show the effectiveness of our theoretical results.