Revealing mistake: In the very beginning when we are flying over the dead town in a helicopter, look closely at one of the very first shots of the "empty" city. On one of the left side streets you can see a car driving down the road. It's not a character mistake because she is looking hard out the window and should have spotted the moving car.
Visible crew/equipment: Very close to the beginning of the film, when they first land the helicopter in the abandoned city, there is an alligator on the steps of a bank. A few seconds later when a zombie comes out of the bank and the alligator runs down the steps, you can see a red band covering his mouth (that wasn't there before) to prevent him from biting the actor. (00:04:05 - 00:04:50)
Revealing mistake: Just after Rickles has his face torn off, you can see that there are no veins on the side of his eyeballs.
Continuity mistake: When Miguel opens the gate a herd of zombies come in. Later, when some zombies come from the bunker where they kept the specimens, several of the zombies are the same, and an obvious one is a kid in a football uniform. The zombies in the bunker had no way out, so how could the zombies be in two places at once?
Audio problem: When Miguel and Steele are collecting some more of the zombies, Steele says 'Nice hat, asshole,' and laughs. Watch carefully at the end bit: they dubbed a laugh into the movie, but it's painfully obvious that his mouth doesn't move as he does it.
Revealing mistake: In the very beginning of the movie, Laurie Cardille is sitting looking at a wall with nothing but a calender on it. She rises and walks up to the wall to get a closer look at the calender. Suddenly hands come out of the wall. If you look closely, you can see the round marks on the "cement" block wall where the hands will come out. Viewed best when freeze framed (which is permitted for a revealing shot such as this one), just before hands emerge.
Factual error: When Steel (the bearded soldier) is cornered by the zombies, he realizes he's doomed and shoots himself in the head. The problem is he is using a Colt M1911 series handgun and the hammer was up when he shot himself. The gun has to be cocked before it can be fired. (01:30:00)
Continuity mistake: At the climax of the film when the military guy shoots himself through the mouth to avoid being eaten alive, the closeup shot of him killing himself leaves a huge spatter against the wall he is in front of. In the next shot where he is falling to the ground, the fresh blood splatter is gone (or, at least, very less apparent). (01:30:25)