The magnetoelectric (ME) coupling on spin-wave resonances in single-crystal Cu2OSeO3 was studied by a novel technique using electron spin resonance combined with electric field modulation. An external electric field E induces a magnetic field component mu H-0(i) = gamma E along the applied magnetic field H with gamma = 0.7(1) mu T/(V/mm) at 10 K. The ME coupling strength gamma is found to be temperature dependent and highly anisotropic. gamma(T) nearly follows that of the spin susceptibility J(M)(T) and rapidly decreases above the Curie temperature T-c. The ratio gamma/J(M) monotonically decreases with increasing temperature without an anomaly at T-c.