The long‐time behavior of charged particles in plasma turbulence with uniform broad wave spectrum is studied numerically. The diffusivity of the particle velocity distribution is characterized by the quasilinear nature for extended time, while a transient diffusion precedes with the enhanced nonquasilinear diffusion rate when resonance overlapping is relatively weak. The observed long‐time quasilinear diffusion coefficient eventually decreases due to the finiteness of the resonance region. The transient‐type diffusion is revealed only by the higher‐order numerical calculation.