Think about why mom might be against your friend. Maybe she's afraid that affected your studies. Try not to give grounds for such fears: show your mom good grades and diligence in study. In General behave so to my mother, there was no reason to say: "This guy's a bad influence".
If you suspect that mom may not like the behavior of your boy think maybe she's right. Mom was much more the case with boys and understands them better. Maybe she'll notice something not noticed you. Besides, you may be in a difficult situation, the advice of a smart older loving friend.
To make it easier to talk to mom about your friend, start from afar. Ask her about youth, than she was fond of who were friends. Gradually move the conversation to the boys: if she was seeing them up to your dad what they were, what was the reaction of her parents...
If the mother is willing to share their memories of first love, can you tell her that you are caring boy and he like you too. Ask permission to invite him to lunch.
If she will let you know it's too early to think about such things, you can introduce your friend as a fellow student with whom you are together doing homework. It is better that your mother know your friends. If the boy will give your parents a good impression, it will be easier then to tell you that you go to the cinema or to the disco.
Perhaps mom is afraid of the consequences of your relationship that you're too frivolous and naive. Try to prove that you are a serious, responsible person you can trust. Take some of the work and follow them precisely and accurately.
Your friend is also better to try to make a good impression on your family. If you let him, he will do so. Gently let him know that you may like or not like your mother, so he avoided mistakes.