  We theoretically investigate the coexistence of antiferromagnetism and
superconductivity in the iron-based superconductors by using the mean-field
theory for two- and three-orbital models. We find that both the s_{+-}-wave and
s_{++}-wave superconductivity can coexist with antiferromagnetism in the two
models. On Dirac Fermi surfaces emerging in the antiferromagnetic phase, a
superconducting-gap function has a node for s_{++} wave but is nodeless for
s_{+-} wave. On the other hand, the gap function on non-Dirac Fermi surfaces is
either nodeless or accidentally nodal, depending on the parameters of pairing
interaction, which is independent of pairing symmetry.
