Yes this is because your body is going through changes.
Not only is it normal for a 5 year old girl, after puberty starts it's normal for a girl of any age. It's also normal for a guy of any age.
your body probably relates your bedroom as a sexual place where you, most likely, masturbate usually so its totally normal
i feel like that and i just sit on my bed and relax my body and i dont feel like it after 5 mins