We report a case of a 24-year-old acute encephalitis patient presenting with epileptic seizures. Glial tumor was suspected due to initial changes seen on magnetic resonance imaging. The findings of electroencephalography (EEG) were indicative of a functional impairment, therefore additional tests were performed that revealed changes characteristic for inflammation. In this case of histologically unconfirmed diagnosis of brain tumor, EEG became the most significant method for suspecting atypical encephalitis. The article also reviews similar cases described in the literature and EEG changes characteristic of infectious and autoimmune encephalitis.