Experiments were carried out on the electric charging of particles in a powder bed with positive ions and/or electrons, which were generated by an atmospheric pressure plasma jet. Here, the effective electric charging area was set to be approximately 0.01 m2 by supplying 1 SLM (standard liter per minute) of helium gas. The upper layer particles of a dielectric powder bed (PTFE) reached equilibrium charging after a few seconds, while the lower layer particles were gradually charged, and the particle charge approached the equilibrium value in 1 min. It was found that the charges migrated up to a depth of 2 mm in the powder bed, and the lower layer particles had larger equilibrium charges than the upper layer ones. In addition, it was found that charging is difficult for particles that do not have very high electrical resistivity (manganese ferrite). However, the lowest layer particles could be charged by placing a dielectric plate under the powder bed.