Clustering is one of the promising technologies for group mobility in mobile vehicular networks. MPAC (Mobility Pattern Aware Clustering) mechanism is proposed in this paper. MPAC aims at improving the stability of the cluster depending on GR (Group Relation), which is derived from some basic mobility metrics such as speed, direction, acceleration and vehicle location. The cluster formation and cluster maintenance operation based on the above mobility metrics are defined. Simulation results show that MPAC has obvious performance advantages in cluster stability, which is illustrated by the mean number of cluster reconfiguration and the mean life time of cluster heads.