The purpose of this paper is to investigate numerically the dispersion characteristics and guiding mechanism of electromagnetic waves in a multicomponent magnetoplasma. The problem is very important in exospheric raio wave propagation. Dependence of group velocity on wave frequency is plotted with wave normal angle as a parameter for plasmas with different ion compositions. The guiding mechanism due to magnetoionic ducting is also discussed at VLF-ELF-ULF whistler frequency ranges in the exosphere. Especially the effect of ions appears very serious in ELF frequency range. Simple considerations are given for newly observed ELF whistlers.