Well it might be towards the lower end of average but it's certainly nothing to get concerned about. If it drops to below 50 I'd start taking a bit more notice, but even then, as long as you aren't feeling tired all the time even when resting, hard to believe that it's anything other than natural variation.
Obviously take this not-a-medical-doctor's medical advice with a pinch of salt, but if Sqad picks up on this I feel fairly confident he'd say the same sort of thing.