As long as you both keep things between you as just friends, then I don't see why not. Friends should be able to hang out with each other! Although if you are worried about your boyfriend being jealous, you might want to tell him about it first. I'm not saying to ask for his permission (because that's stupid; you don't need anyone's permission to hang out with friends) but instead to tell him about it so he doesn't think anything fishy is going on.
But if your boyfriend still thinks that it's too much and prevents you from hanging out with this friend, then you may want to reevaluate your relationship with your boyfriend....