Plasma Waves may propagate in different frequency levels. This study justifies the reason for the difference in dispersion curve at low and high frequencies of plasma wave propagations. At low frequencies i.e. ( ), the right handed and the left handed waves tend to the Alfven wave. The fast and slow Alfvén waves are indistinguishable for parallel propagation whereas the shear-Alfvén wave does not propagate perpendicular to the magnetic field. At high-frequency the right-handed waves, propagating parallel to the equilibrium magnetic field, and oscillating at the frequency are absorbed by electrons. By this paper it is proved that the low-frequency branch of the dispersion curve differs fundamentally from the high-frequency branch, because the former branch corresponds to a wave which can only propagate through the plasma in the presence of an equilibrium magnetic field, whereas the high-frequency branch corresponds to a wave which can propagate in the absence of an equilibrium field.