Fleas are not uncommon for people who have pet dogs or cats. However, can pet mice get fleas? The simple answer is yes they can. Although, there is a very small chance of that happening if you do not have any outdoor pets that come into contact with your pet mouse. Furthermore, not letting your mouse go outside (even in a cage) will reduce the risks of them getting fleas. That is not to say that a pet mouse will never get fleas, they have fur, which is a huge pre-requisite for them.
It may not always be obvious when your mouse has fleas, but there are a few things that are big signs. For example, they will scratch themselves a lot, much like other animals. Furthermore, there may be spots of blood on them, or in their enclosure showing the fleas are biting them. Flea treatment for mice is similar to that of any other pet. However, you are best to talk to your vet about which product is best for your situation and how often to use it.