  The existence of null circular geodesics has been proved in the background of
non-extremal spherically symmetric asymptotically flat black holes in previous
works. Then it is an interesting question that whether extremal black holes
possess null circular geodesics outside horizons. In the present paper, we pay
attentions to the extremal spherically symmetric asymptotically flat hairy
black holes. We show the existence of the fastest trajectory to circle a
extremal black hole. As the fastest trajectory corresponds to the position of
null circular geodesics, we prove that null circular geodesics exist outside
extremal spherically symmetric asymptotically flat hairy black holes. We also
point out that our proof also works for non-extremal black holes.
