beta wave

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The second most common waveform occurring in electroencephalograms of the adult brain, characteristically having a frequency from 13 to 30 cycles per second. It is associated with an alert waking state but can also occur as a sign of anxiety or apprehension.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun neurology An electrical signal produced by the brain while the subject mentally active.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the normal brainwave in the encephalogram of a person who is awake and alert; occurs with a frequency between 12 and 30 hertz