In this paper, we study the monotonicity of parabolic frequency motivated by Baldauf and Kim (Parabolic frequency on Ricci flows. To appear in Int. Math. Res. Not., rnac128. https://doi.org/10.1093/imrn/rnac128) under the Ricci flow and the Ricci-harmonic flow on manifolds. Here we consider two cases: one is the monotonicity of parabolic frequency for the solution of linear heat equation with bounded Bakry-Émery Ricci curvature, and another case is the monotonicity of parabolic frequency for the solution of heat equation with bounded Ricci curvature.