Is it normal to freak out in front of the opposite sex?

when I see good looking girls I try to avoid them but sometimes it's awkward to ignore them so I have to talk or at least acknowledge them. That's when it gets weird, because I try to give off the appearance of being calm and relaxed, but inside I freak out. Usually in this situation I just can't say much of anything, and anything I do say turns out to be really stupid. I am a pretty funny and smart guy, my friends think so. But when I am faced with attractive girls, I just can't show my "real" personality, it's like my brain stops working, and instead I start trying to be cool or pretend like I don't care, when in fact I do care what she thinks of me and instead of trying to make her comfortable around me or say something funny or intelligent, I'm more concerned with my appearance and how I look or the image I project at that exact moment. Basically I get really self-conscious because I am trying too hard to impress someone and that prevents me from just relaxing and being myself. A lot of times I even think about what I could have said or how differently I could have acted afterwards when I'm alone.