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 μ₀Hⁱ = γE along the applied magnetic field H with γ = 0.7(1) μT/(V/mm) at 10 K. The ME coupling strength γ is found to be temperature dependent and highly anisotropic. γ(T) nearly follows that of the spin susceptibility J^M(T) and rapidly decreases above the Curie temperature T_c. The ratio γ/J^M monotonically decreases with increasing temperature without an anomaly at T_c.