In this work the effect of H-2 on the electrical properties of H-ZSM-5 and Pt/H-ZSM-5 has been studied applying impedance spectroscopy in order to clarify the nature of migrating H* species (charged or uncharged, atomic or molecular) in the spillover process. The observed drop of the resistive part of a charge carrier relaxation process is attributed to the increase of mobile charges in the zeolite. This can be explained in terms of the dissociation of hydrogen on the Pt nanoparticles, the subsequent diffusion onto the zeolitic support and the formation of H+ as migrating species.