Continuity mistake: The Nurse Zombie and Sweater Zombie are outside of the mall, then, inside of the mall. Thus, they are among the zombies eradicated after the doors are blocked. But, they are among the zombies that invade the mall and eventually make it onto the roof.
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 Reiniger 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.
Continuity mistake: When Roger and Peter are blocking the entrances with the trucks, Roger kills a zombie with a long beard that is walking towards him between the trucks. Later on in the movie, we see the same zombie, in the same clothes, outside the doors, trying to get in. (01:07:35 - 01:17:15)
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. (00:22:55)
Continuity mistake: In the beginning of the movie at the TV studio, Peter tells Fran that they are meeting at 9:00 to take a helicopter out of town. When they take off in the helicopter and fly away, there is a giant digital clock on a building in the background that reads 6:00. (00:05:05 - 00:18:50)
Continuity mistake: After parking the first truck in front of the mall doors, Roger jumps out and runs towards Peter's truck. Notice the zombie wearing the red and black striped rugby shirt. After Roger runs past him, he breaks zombie character and becomes concerned about his shirt being tucked in. (01:00:50)