Is it normal to dream "sexually" about your best friend?

Hello, i've known this is girl who i call now my best friend for about 3 years. She's been very close to me through thick and thin for a long time and we always keep it real with eachother. I never have any thoughts or fantasies of "hooking up" with her, matter of fact im going out with her sister so i'm far from that. Today, I had a small nap and i had a pretty extreme dream about my best friend and i woke up with a major WHOA! Is this normal or is there something going on?