[wonderbread]

Does she know that you have friends online? Does she know which site he is from or how you met him? If so, I would just casually bring it up. Just be like you know that site that I am on, well I am friends with so and so and we are close. Then if she ask questions from there answer them. Then if she doesn't ask if you like him, volunteer the information and tell him that your sorta closer then friends or whatever you two are. She may be wary but you can try to reassure her that everything is fine and if things get weird or creepy that you will not continue to talk to him.

I know how you are probably feeling. I had to tell my mom about my first "close internet friend" and I was freaking out and one day when she was dropping me off at class we just started talking about it.