Abstract: Electroencephalography (EEG) signal is one of the important scopes to diagnosis epilepsy, which is a recording of the electrical activity of the brain from the scalp. Algebraic structure of EEG signals during epileptic seizure can provide valuable insight and improve understanding of the mechanisms causing epileptic disorders. EEG signals during epileptic seizure can be viewed as a semigroup of square matrices under matrix multiplication. In this study, an element in that semigroup is shown to be regular.