Yes it is, but then again, I don't think you should get into a relationship with your best friend unless you guys could break up and still be best friends. I have done that, and we are still best friends. You guys have to make sure that if you break up, your relationship as best friends will still remain to stay strong.
Yes, it's even better to have a relationship with a ever good Friend this type of relationships last a lot longer and there's more trust in them because of the bond made before becoming into a couple! Good-luck