  We examine the spin and charge excitations in antiferromagnetic iron
pnictides by mean-field calculations with a random phase approximation in a
five-band itinerant model. The calculated excitation spectra reproduce well
spin-wave dispersions observed in inelastic neutron scattering, with a
realistic magnetic moment for CaFe$_2$As$_2$. A particle-hole gap is found to
be crucial to obtain consistent results; we predict the spin wave in LaFeAsO
disappears at a lower energy than in CaFe$_2$As$_2$. We analyze that the charge
dynamics to make predictions for resonant inelastic x-ray scattering spectra.
