Abstract— Multi-agent systems (MAS) have received an increasing attention over the past few years. Here an MAS is a system consisted of multiple interacting intelligent agents. This paper further investigates the consensus of MAS with an active leader and asymmetric adjacency matrix. In particular, the state of the active leader is changing and unmeasured. Under some suitable conditions, we have proved that: i) each agent of MAS can follow the active leader if the input of the active leader is known beforehand; ii) the tracking error of MAS can be effectively estimated if the input of the active leader is unknown beforehand. Moreover, numerical simulations are then given to verify the effectiveness of the proposed theorems.