@Virginia524 What would be your reason for doing so? It isn't okay unless there is some emergency situation, like the plumbing just burst or the place is on fire. Guests rightly feel uncomfortable or downright mad about such things as a host entering when they aren't there. If you need to go in to do a repair, or something like that, you need to arrange a convenient time to do so with the guests, preferably when they are home, because you don't want to take the chance on a guest accusing you of stealing something or rifling through their belongings.
Guests have an expectation and a right to privacy.