Ballistocardiogram (BCG) signal is created by the movement of the blood in the body, and has been recorded via standing on a force platform. Prolonged quiet stance is well understood to induce postural sway. Previous work has shown that blood pressure (BP), posture muscle activation (EMG) and center of pressure (COP) signals are related during quiet stance. In this study, we investigated the relationship between the BCG and BP, EMG and COP signal pairs to address the central question whether the BCG signal is associated with cardio-postural interactions during orthostatic challenge. The wavelet transform coherence method was applied to obtain time-frequency varying estimate of the coherence between the signal pairs. The significant (>threshold) and time-varying coherence found in the three frequency ranges (0.1–0.5, 0.05–0.1, & 0.01– 0.5Hz) suggested the presence of a time-frequency dependent relationship between the signal pairs. The results from this study highlight a potential interaction of the BCG signal with other relevant physiological signals during orthostatic challenge.