Introduction: Time perception is one of the most controversial issues in the field of cognitive science. One of the first models for time perception in the brain is the internal clock model, according to which a part of the brain acts as the constructor of time pulses and another part as the counter of these pulses. Yet, nother part is responsible for storing this time in memory. According to previous studies, delta and beta waves seem to play a role in the overestimation and underestimation of individuals, although the role of these waves in the perception of long- term time frames has not been studied.Method: Participants in the test were 33 healthy subjects and according to the way of estimating time, they were placed in two groups of overestimation and underestimation. Time estimation was investigated during a mindfulness task. Functional brain activity was investigated using electroencephalography during rest and task. Spectral analysis was performed in the standard bands at 19 electrodes. Statistical analysis was carried out for five electrodes of C3, C4, Fz, Cz, Pz. The statistical comparison of five C3, C4, Fz, Cz, Pz electrodes showed a meaningful difference between the two groups in the absolute power of the beta frequency band (25-30 Hz) on each of the five electrodes.Results: The results show significant differences of high beta (25-30 Hz) absolute power at all investigated electrodes.Conclusion: The results can be argued in the context of internal clock model and scalar timing theory. In the range of long term duration, the results confirm internal clock model as a valid model for explaining time estimation.