Several variables are considered when you apply for a mortgage, your credit score is an important one.  Generally, the better your credit score is, the lower your interest rate will be.  Your credit score, however is not the only factor considered. Other variables such as your debt-to-income ratio and downpayment amount are also important.
Even though there is no “official” minimum credit score, it will be easier to obtain a mortgage if your score is higher—and the terms will likely be better, too.