funny you mentioned this... i just talked to my bf, and he was saying that his friends think i'm anti-social and dislike them, just because i'm a little more quiet and reserved than they are! i'll admit that i am rather shy when meeting new people, and especially in larger groups. i wouldn't say i'm anti-social... i'm just not very outgoing, and i've always been this way. when i was growing up, i was somewhat of a loner, had very few friends, and was always doing things on my own.
as an adult, i have no problems making friends.. it takes me awhile to feel comfortable enough to open up and be more talkative around them... but i tend to be more of a listener than a talker. i have a handful of close friends, and many acquaintances that i've met through mutual friends. it really depends on the person i'm talking to... if i can find something in common, i can be really chatty... otherwise, not so much.
i don't think it's necessarily a disorder either... i'm sure if you feel that it is really a problem and hinders your daily life, you can get it checked out.