Micro-Doppler (m-D) signatures induced by micro-motion dynamics, which are of great importance for target classification, have received increasing attention among the radar community. For scenarios when the micro-motion of radar target is accompanied by macro-motion, the periodicity of m-D is disturbed by macro-motion. In that case, extraction of micro-motion signatures based on the periodicity of time-frequency representation (TFR) of the radar echo may become invalid. In this work, we show that the periodicity of TFR is replaced by circular periodicity in the presence of macro-motion. In view of this, the circular correlation coefficients of TFR are employed to characterize the circular periodicity of TFR and to provide an estimate of the micro-motion period. The property of circular correlation coefficients enables us to estimate the micro-motion period of radar targets in the presence of macro-motion. Experiments with synthetic data and measured radar data validate the effectiveness of the proposed method.