Visible crew/equipment: Very early on in the movie, Neville is happily driving around the deserted streets. Half way through this scene the camera shows us Neville's view out the front windscreen of the car. Ahead, moving cars can be seen crossing the intersection, obviously where the streets hadn't been blocked off for the filming of the movie.
Other mistake: In the opening scene where Charlton Heston drives into a Deserted Los Angeles, he drives past at least 3 people walking down the sidewalk. The first person he passes is quite visibly holding up the traffic for the shooting. Another can be seen on the left of the screen when Heston puts the tape on. And one more can be seen in the wide shot of the street. Other than this, the film makers did a great of making LA look deserted.
Other mistake: Early in the movie, when Neville wrecks his car he takes the gas can out of his car and starts walking down the street. As he does they switch to a wide view of the city in which you see about three city blocks. When you look at the only "through" street in the shot, there is a car making a left hand turn about three blocks down that street and just behind the car is the freeway overpass with two or three cars passing on it, before the shot ends.
Continuity mistake: In at least one scene, traffic lights are shown flashing. Where's the power coming from?
Continuity mistake: When Lisa sees the family marching towards Neville's house, in front of the building on the left is a waste can and a mail box on the opposite corner. When Neville drives by the same building a short time later, there is now a dark car parked in front, two other cars parked on the sidewalk further down the street, and the mail box has moved across the street by the door. (01:25:05 - 01:27:00)