Continuity mistake: After the cast makes a getaway on the double decker bus, the little kid jumps on John's back and says, "Nice job." When the shot cuts, he is still there. In the next shot, the bus is pulling over to the side of the road and the boy is not on John's back anymore.
Continuity mistake: When one of the men in red is looking at the pygmy in the tree, the pygmy's face is looking up slightly (right before the first man is attacked) and has his mouth relatively open. But, right before it wakes up, its head is slightly down, and the mouth is less open than it was before.
Continuity mistake: When Rick turns around finds Alex, Alex falls back and his hat falls off and rolls back a few inches, resting a few inches from the top of his head. However, after Rick says his name, it cuts back to Alex and the hat is practically under his head, almost behind his back.
Continuity mistake: During the scene when Imhotep controls the water and raises it up he starts with straight arms, as shown in the shot with his back facing the camera. However in the next several shots showing him from the front he has bent arms, then straight arms from the back again.