A beam source for production of active species, with translational energies in the sub-eV region, has been constructed and characterization of their beams has been made. The source employs microwave plasma discharge of a dilute mixture of molecules in rare gas at relatively high pressures (< 200 Torr). So far, a variety of atomic beams, O, N, H, Cl, etc., has been generated with high degree of dissociation from the admixed molecules. Although the beam stagnation temperature does not exceed 2000 K, average translational energy can be varied by a choice of the buffer gas. Under the conditions of normal operation (microwave power of 60-80 W), average translational energies up to 1.0 eV of atomic beams with Mach number ≤ 5 have been easily obtained when He is used as the buffer gas. From the intensity levels of crossed beam-chemiluminescence observed using this beam source, it was found to be applicable for production of electronically excited species, e.g. metastables of rare gas and nitrogen atoms.