I am interested = Someone or something (for example a beautiful woman; a striking work of art; a fascinating story; an unusual mechanical device) has engaged my interest and my attention at this very moment. Of course, if for some reason I lose interest, I will no longer find myself being interested by that person or thing.
Note that both of these are very odd things for anyone to say. What you probably want to say is the far more ordinary and normal "I am interested [in/by X.]