Abnormal EEG waves indicate a problem in the electrical activity of the brain, according to Healthgrades. EEG waves during a seizure show a sudden change in brain activity, while a general abnormality in the size or shape of the waves indicate other neurological disorders.
An EEG, or electroencephalogram, is used to diagnose epilepsy as well as other brain conditions, including head injuries, strokes and brain tumors, notes Mayo Clinic. EEG results may pinpoint an abnormality in a particular area of the brain, according to WebMD. If the chemical balance of the body is affected by an infection, a metabolic disorder or drug intoxication, EEG waves throughout the brain may be abnormal. A "flat"' EEG, showing no electrical activity, is seen in coma and sometimes in medically induced sedation.