Is it normal that i keep it a secret..

I've been masturbating for a while now, and my mum doesn't know (at least I don't think she does). The thing is, is that I want to know if it's normal to not want to tell her? She thinks I do nothing like that kind of thing, and I would feel very embarrassed telling her that a masturbate and even watch porn now and then. It's starting to get a bit awkward when I go upstairs, and my mum questions why I go up there for long periods of time and then say I was doing something. She hates me keeping secrets from her. Is it normal to feel embarrassed to tell my mum I'm not as innocent as she thinks?