High electromyography (EMG) activities are artifact signals that occur within the frequency “range of interest” of the bispectrum, because EMG frequencies overlap the Bispectral Index algorithm’s Relative BetaRatio descriptor in the 30–47 Hz range. Although the EMG power spectrum is quite small in relation to the total EEG power spectrum (0.5%), it is estimated that the electromyography EMG30–47 Hz portion to be one-tenth the magnitude of the electroencephalography (EEG) EEG30–47 Hz signal in the Bispectral Index algorithm. Contamination of processed Electroencephalography-Depth Of Anesthesia (pEEG-DOA) indices in general and Bispectral Index in particular by EMG activity is therefore “inherent” in the calculation of the Bispectral Index value, because frontal Electromyography (fEMG) frequencies could simulate EEG frequencies, in particular the 30–47 Hz component of the Relative BetaRatio subparameter that is typically associated with awake or a light level of anesthesia. Thus, EMG contamination during deep anesthesia in patients who generate little EEG power in the 30–47 Hz range may erroneously mimic the EEG of awake subjects; this will make patients under deep anesthesia appear more awake than they really are that would be misinterpreted by the pEEG-DOA algorithms as EEG activity and assigned a spuriously elevated Bispectral Index value. The administration of neuromuscular blocking agents (NMBAs), in that case, would then decrease the Bispectral Index value by alleviating the artifact of high EMG activity from muscles lying near the electrodes, thus “unveiling” the true calculated Bispectral Index value. The Entropy algorithm uses spectral analysis to produce two main Entropy parameters for assessing depth of anesthesia; the State Entropy (SE) indicates the depth of hypnosis with an index scale from 0 to 91, and the Response Entropy (RE) indicates nociception/responsiveness to stimuli derived from the fEMG, with an index scale from 0 to 100. When the difference between RE and SE widens, this indicates inadequate anesthesia. The EMG32–47 Hz signal overlaps Entropy’s indices RE EEG0.8–47 Hz but not SE EEG0.8–32 Hz. The EMG artifactual EEG signal contamination results in an increase in both Entropy and Bispectral Index with neuromuscular block reversal.