Definitions for "Beta waves"
Brain waves indicating normal waking state with consciousness directed to the external environment.
These are found mainly in adults who are awake, alert, whose eyes are open and who may be concentrating on some task or other activity.  They are most reliably recorded from the front and middle of the scalp, and are related to activity in the sensory and motor cortex.
'Desynchronized' high-frequency (20 Hz) waves seen in electroencephalogram in mentally active subject.