Power-bus resonance of printed circuit board causes propagation of electromagnetic noise and detraction of power integrity. For suppressing the power-bus resonance at higher frequencies, we proposed a lossy resonator filter consisting of an open stub covered with magnetic thin film. First, this paper introduces the concepts of the proposed filter, especially focusing on the impedance characteristics. Then, the suppression of powerbus resonances by the proposed filter is demonstrated through full-wave simulation. As a result, it was found that the magnetic thin film formed on the open stub is promising for applying a little loss to the proposed filter. Also, full-wave simulation with an AC equivalent model demonstrated that the proposed filter achieved the desired suppression at higher frequencies over 1 GHz.