Revealing mistake: After Rick and Evie find the bracelet the water starts coming after them. There are then shots of the water and then them running. Finally, they stop and hold each other. Shortly after that the wave comes over them. If you notice right before it hits them, it is their doubles you see. Not the actors. (00:14:55)
Visible crew/equipment: When Ardeth, Rick and Evie arrive at the first city where Imhotep took their son, Evie is walking through the hall where she had the vision of fighting with Anuk-Sun-Amun in her previous life. As she's walking past/behind a column, you can see someone's head and shoulder poking out from the back side of the column. (01:14:57)
Continuity mistake: In the scene where the bad guys ask John Hannah about the bracelet of Anubis (and he has no idea what they're talking about), they throw him on a chair, and one of the guys in red holds a knife to his throat. In the shots from the front, he also grabs John Hannah's hair with his other hand, in almost all of the shots from behind, he doesn't. (00:25:50)nightline
Continuity mistake: When they arrive at the Magic Carpet, in the very frame where the camera is on Rick and you can hear Izzy lock the doors, Jonathan is seen walking towards Rick, and he gets very close to him. The camera then cuts to the locked doors, and when it cuts back to Rick and Evie you can see Jonathan walk all the way from the car door back towards Rick - for a second time. (00:54:04)
Revealing mistake: In the scene where Rick and Evie break through the wall together with the water (after their son made the columns fall), you can see that Evie is lying on a skateboard on which she's being pulled forward. (It's a black one, visible when she leans over to Rick.) You can also easily see it under Rick. (00:16:10)
Factual error: When Rick and Jonathan (in his mysteriously foam free tux, as noted elsewhere) vault over the fence outside Rick's house, a thug is firing at them with a machine gun from an upstairs window. Look at the bullet impacts on the top of the fence - some of them could only happen where they do if the bullets had passed straight through Jonathan's body.
Revealing mistake: The Anubis Warriors do not leave footsteps in the sand, but they do kick it up when they run. This is especially obvious when the army turns to dust at the end of the movie, leaving a pristine, footprintless desert. One could argue that the dust from the disintegrating Warriors covers the footsteps, but the dust also engulfs the Medjai, whose footsteps are still visible when they cheer.
Visible crew/equipment: You can see this mistake in the double decker bus scene. The bus suddenly turns left (right on the screen cause this is a front take) and hits a car that is parked in the street. If you look closely, you can see that the wheels of the car don't move because the car is mounted on a wheeled surface. (00:43:40)
Factual error: After Evie is stabbed and dies in Rick's arms, if you look closely at her neck, you can still see a pulse in her neck. Dead people don't have pulses. Yes, obviously they couldn't have actually killed her for the shot, but at the same time they shouldn't have had a close-up of her neck either... (01:33:05)
Continuity mistake: During the long shot when the cast are racing across Tower Bridge in the double decker bus, right in the middle of the screen you can see the twinkling lights of a distant skyscraper which looks suspiciously like Canary Wharf, which of course had not yet been built in 1935. Its construction was in fact not completed until 1990. (00:45:05)