The Beast is one of the names in Scripture that refers to the Antichrist. He is also called the Beast From The Sea in Revelation 13:1, pictured as a seven-headed beast with one of its heads fatally wounded and yet miraculously healed, causing the world to marvel at the beast and worship it, saying, "Who is like the Beast? Who is able to make war against him?" The Beast is also given great power and authority over all the people on the earth to make war with the saints and to overcome them for 42 months. He speaks evil and blasphemous things against God and His name, His tabernacle, and those who dwell in heaven. The Beast From The Earth, also called the False Prophet, is the Beast's servant, given power from him to perform great deceiving signs, to give breath to the image of the Beast so that it should speak and cause as many as would not worship the image to be killed, and to cause all people to take a mark upon their right hand or their forehead so that no one can buy or sell unless they had the mark.
In the Left Behind books, it also refers to a powerful supercomputer in Belgium, though it has no relation to being the Antichrist.