  We explore theoretically impurity states in the antiferromagnetic
spin-density wave state of the iron arsenide. Two types of impurity models are
employed: one has only the intraband scattering while the other has both the
intraband and interband scattering with the equal strength. Interestingly, the
impurity bound state is revealed around the impurity site in the energy gap for
both models. However, the impurity state is doubly degenerate with respect to
spin for the first case; while the single impurity state is observed in either
the spin-up or spin-down channel for the second one. The impurity-induced
variations of the local density of states are also examined.
