In this paper, an error concealment algorithm is proposed to conceal an entirely lost frame in an H.264/AVC compressed video bitstream. For a lost frame, the algorithm reconstructs the lost motion information of this frame based on its temporal neighbors. The algorithm is block based and thus has low computation and implementation complexity. It is designed for those hard-to-conceal video sequences, which have abundant active and chaotic motions. Experimental results show that the algorithm compares favorably to other simple error concealment algorithms