ANY time you have sex -- regardless of the method of birth control you're using -- there is ALWAYS a chance of pregnancy
And for the record, withdrawal method ("pulling out") is one of THE WORST methods of "contraception" there is. In fact, it doesn't even rank as moderately reliable! You have a 1 in 4 chance (or 25%) of getting pregnant EVERY time you use this "method" as contraception.
So if you want to have sex and do NOT want to get pregnant (as I would take from the tone of your question), then GET ON THE PILL or USE CONDOMS, or DON'T HAVE SEX!
EDIT: Mother Nature has a WICKED sense of humor. ASSuming that you can "only" ovulate at mid-cycle is only going to make a ...well you get my point. DO NOT fool around with sex unless you're willing to pay the price.