  The magnetic excitation spectrum of the unconventional ferromagnet
CeRh$_{3}$B$_{2}$ was measured by inelastic neutron scattering on single
crystal sample in the magnetically ordered and paramagnetic phases. The
spin-wave excitation spectrum evidences high exchange interaction along the
c-axis about two orders of magnitude higher than the ones in the basal plane of
the hexagonal structure. Both strong out of plane and small in plane
anisotropies are found. This latter point confirms that considering the $J$=5/2
multiplet alone is not adequate for describing the ground state of
CeRh$_{3}$B$_{2}$. Quasielastic scattering measured above $T_{Curie}$ is also
strongly anisotropic between the basal plane and the c-axis and suggests
localized magnetism.
