Continuity mistake: When a zombie's head is held up in the truck to be shot, there is a big splatter of blood down on the face of the soldier. He wipes a very small amount of blood off, but when he gets into the other truck he is perfectly clean.
Visible crew/equipment: After the main characters have entered the mall through the skylight, and have gone down the stairway in order to secure the mall, Scott Reineger and Ken Foree open the door into the corridor leading to the control room and boiler room. Whilst walking through said doorway, there is movement in the shadows in the top left. This has to be a crew member, as the only other zombie that is in this area is in the boiler room.
Other mistake: In the aerial shots of the semis being driven in the mall parking lot, the zombies are milling about. Notice they have left a path just clear enough for the truck.
Continuity mistake: When the Sweater vest zombie first goes up to the 2nd floor he appeared coming up to the 2nd floor moments later.
Factual error: When they are refuelling the helicopter (as a zombie approaches quietly from behind) the actor has put the gas nozzle not into the hole for the gas tank, but into one of the foot-holes that helicopter mechanics use to climb up to the top of the helicopter to do repairs. It doesn't even fit properly.
Revealing mistake: When the bikers are grabbing their weapons, we see a grenade. You can tell that it is fake because the bottom is bored out.
Continuity mistake: When the bikers are in the mall, a zombie is killed next to a teepee. Another zombie is pushed into the teepee knocking it over. As it falls, you can see the first zombie starting to roll out of the way.
Continuity mistake: Near the end, Steven is in an elevator, and the zombie opens the doors and starts biting him. When he gets them all out of the elevator, blood comes out of his mouth and down the right side of his face. But later the elevator doors open and Steven is a zombie and the blood is on the left side of his face.
Continuity mistake: At the TV station, when Fran takes control of the camera, notice a man with a sweater and a beard behind her, but in the very next scene the same man appears with a different shirt on.