I've gone to the stateroom a couple of times while it was being cleaned to get things, and the room steward is always there while the room is being cleaned. They do prop the door open, however, but their cart and vacuum is usually in front of the door, so it would be difficult to get in without being noticed.
But as ZooMommy said, if you are concerned, you could put the laptop in the closet. Or under the bed.