Human beings and control centers are usually far away from each other, so cyber attacks on the sensor measurements can lead to loss of user privacy, information, and trust. Driven by this motivation, this letter proposes an Internet of Things (IoT)-based human motion estimations algorithm under cyber attacks. The sensing measurements are transmitted to the control center over an unreliable communication channel where cyber attack occurs. Based on the mean squared error, the optimal state estimation algorithm is derived to estimate human motions. Simulation results show that the proposed method provides significant performance improvement compared with the existing approach.