Let $G=K_{n_1,n_2,...,n_r}$ be a complete multipartite graph on $\left[n\right]$ with $n>r>1$ and $J_G$ being its binomial edge ideal. It is proved that the Castelnuovo-Mumford regularity $\mathrm{reg}\left(J_G^t\right)$ is $2t+1$ for any positive integer $t$.