To interact with a dynamic environment, anticipating “when” an event occurs is crucial to perform the desired actions at the right time. Recent lines of research have suggested that such temporal predictions could be implemented through the entrainment of slow neural oscillations (e.g. delta, 0.5 – 4 Hz). Entrainment by the temporal regularities in the environment would thus tune brain dynamics to the predicted onsets of relevant events. However, it is difficult to assess whether entrainment truly results from an a priori endogenous delta oscillation, or whether oscillatory brain dynamics merely reflect the exogenous rhythmic input. To establish whether endogenous delta oscillations can be seen in human brain activity, we re-analyzed an MEG dataset (N = 23) collected for a different experiment. We chose three conditions devoid of external stimulation, yet varying in the amount of internal rhythmic behavior: 1. Resting state (no rhythmic behavior), 2. Motor tapping (overt rhythmic behavior), and 3. Internal counting (covert rhythmic behavior). Combining spectral analyses with a fine-grained peak detection algorithm, we were able to detect spectral peaks in the delta frequency-range. Additional analyses are being carried out to establish whether those peaks can be interpreted as endogenous oscillations. Keywords: Endogenous, delta, neural oscillations, rhythmic behavior, PSD