Continuity mistake: When everyone is running out of the theater, a woman with a red belt and yellow purse can be seen exiting with the other terrified patrons. A few seconds later, the exact same woman is seen running out of the theater again.
Revealing mistake: Joe is much too old to be in high school. He appears to be in his thirties (the actor playing him was 35 at the time).
Visible crew/equipment: When the aliens blast off at the end of the film, the bright light causes the shadows of the actors and vehicles, etc, to appear on the painted backdrop of desert and sky.
Continuity mistake: The interior of the ship is quite spacious, a central atrium on each level, with crew quarters and storage spaces opening off it. Yet, when the two officers take a space-walk down the length of the ship, it appears to have a diameter of less than 20 feet.
Continuity mistake: The sheriff's wagon the 30-foot man picks up is a 1958 Plymouth. But the car that is rolling after he drops it lands on the ground is a 1950s Chevrolet. When the sheriff tries to call for help, the smashed car is the 1958 Plymouth again.
Factual error: This horror-fantasy film (a 1958 knockoff "The Mummy") was inspired by the faceless whole-body plaster casts taken from the volcanic ash of Pompeii, at the foot of Mt. Vesuvius. The running mistake in this movie is the assumption that the faceless bodies of Pompeii were 2000-year-old mummies preserved by volcanic ash and could, thus, be re-animated (by radiation, in this case). The fact is, the victims at Pompeii were originally encased in hot volcanic pumice and ash, and the corpses then disintegrated, leaving hollow "molds" of human bodies underground. It wasn't until the mid-19th Century that archaeologists first discovered the molds, filled them with plaster, then extracted the whole-body plaster casts for display. Since the faceless bodies of Pompeii are nothing but modern plaster casts, there would be nothing to re-animate, by radiation or any other improbable means.
Other mistake: Leonard Nimoy is incorrectly mentioned in the credits as 'Leonard Nemoy'.