Continuity mistake: In the interior shot, when Jasmine tries to explain why she doesn't want Steven to leave she pulls open the white curtains, to view the alien ship through the window (the window closest to the door), and as Steven walks out the front door she stands by that open window. Then when it cuts to the exterior shot, in an instant that window's brown venetian blinds are now down and the white curtains are drawn closed, as Steven walks down the lawn.
Continuity mistake: When Steven is about to head back to El Toro, he tells Jasmine that she and Dylan can come stay with him at the base. Then when they kiss, Steve's head leans to his right - in shadow, then left - with lots of sunlight, and back to right - in shadow again, between shots. (00:30:30)
Continuity mistake: Aboard the AWAC, after the pilot sees the fireball emerging from the clouds, there is a wideshot of the interior with the cockpit in the background. The pilot is not wearing the dome-shaped helmet, note the distinct outline of his hair, whereas in the close-ups he is wearing it. (00:16:10)
Continuity mistake: In the Oval Office, when General Grey says, "They're tracking another one off the California coastline," as Connie rushes in, the lamp on the table beside the couch is gone. Then in the overhead shot of the Oval Office the lamp is back on the table. (00:14:45 - 00:15:50)
Continuity mistake: After going to the bathroom, when Steven turns on the TV in the kitchen, in the TV's close-up before the program comes on, the kitchen's reflection is visible. In the reflection something is lying on the stove (beside the fridge) and a chair is in front of the corner door, but when it cuts to Steven opening the fridge door, they're gone.
Continuity mistake: When the spaceships begin arriving, it is obviously morning in Los Angeles. Will Smith and his girlfriend are still in bed, and later on Will goes out to get the morning paper, etc. Jeff Goldblum has just said that the countdown will be over in roughly 7 hours, so how is it night in LA when the spaceship finally attacks?
Continuity mistake: When Steven Hiller goes out to get the paper, the paper has a string around it to keep it closed, yet he opens it up as if it was only folded. (00:25:15)
Continuity mistake: When Dr. Okun and David are inside of the alien ship, and Dr. Okun shows him the scrolling green lines on the console he says that they don't know what they are. David says it's the same thing as their countdown signal and they always move together. Yet when Steven is flying their ship through the mothership, the lines go horizontal, spread apart, and even turn blue in some parts. (01:21:00)