Submillimeter wave ESR experiments have been performed on Cd1-xMnxTe at x = 0.35. A crossover from the damped ESR signal to the collective spin-wave mode was found around 15 T. In addition to the host resonance, a new peak was observed for the sample doped with 0.3% of Fe together with 38% of Mn. The correlation between the host resonance and the new peak observed in the frequency-field relation indicates the existence of magnetic clusters interacting with host spins.