Methadone has a neurophysiological effect in humans that can be analyzed quantitatively using an electroencephalogram (EEG). This study considers the effects of neurophysiological for delta, theta, alpha, and beta frequency band in all brain regions for two dosage ranges categorized as low dose (<100 mg) and high dose (>100 mg). The EEG signals of methadone patients are compared to the healthy subject to analyze the brain alteration after one-hour methadone administration using resting condition (open-eyes and closed-eyes) test protocol. This study uses 17 channels with 10-20 international standard systems for the electrode caps. This study uses 4th order Butterworth bandpass (0.3-70 Hz) filter and STFT Hanning-window to determine the power spectral density. The results indicate that for low dose methadone patient, all the power spectrum of frequency band increase relative to healthy subjects in all brain regions and still follow the trend of healthy subjects' EEG oscillation. Nevertheless, for high dose methadone patients, only the delta and theta that follow the trend of healthy subject's EEG oscillation, but the value of power spectrum decreases relative to healthy subjects in all brain regions. Further, the power spectrum of alpha and beta for high dose methadone patients has different values for different brain regions.