Sleep bruxism (SB) has been reportedly associated with temporomandibular disorder (TMD); however, solid evidence is lacking. Previous studies have primarily used traditional metrics, such as the masticatory muscle activity (MMA) index and bruxism time index (BTI) to investigate the link between SB and TMD. However, we aimed to examine how the electromyography (EMG) frequency spectrum is associated with TMD in SB participants. We hypothesised that the EMG signal frequencies during MMA events would be lower in SB participants with TMD pain compared to those without TMD pain. In this exploratory study, we retrospectively analysed home polysomnography data from 44 participants who indicated possible SB. The median signal frequencies and absolute power were calculated using the Fast Fourier Transform of the EMG signals during MMA events. Moreover, the MMA index and BTI were calculated, and all parameters were compared between SB participants with and without TMD pain. The results showed that the absolute power and median frequencies were significantly lower in SB participants with TMD pain compared to those without TMD pain (p < 0.05), whereas the MMA index and BTI did not differ between the groups (p > 0.05). These findings suggest that masticatory muscles are getting fatigued in TMD participants with SB and therefore, EMG frequency-based analysis may provide a promising direction for future assessment of TMD consequences of SB. However, these preliminary results should be validated in future studies involving a larger and more heterogeneous pool of participants.