Possibly. You may be experiencing breakthru bleeding or mid cycle, which does sometimes happen though not always present in every woman. If you are sexually active, don't assume if you have bleeding that its your period and you're not pregnant. Check a pregnancy test. If this persists you may have some other causes that your gyn can evaluate in the office.
Not unusual. It is not unusual at all to have irregular bleeding from time to time. Times when you should see a doctor immediately: postmenopausal bleeding, pregnancy. Often you'll see this in the teens or mid/late 40s, switching/starting/stopping birth control, times of stress--but it isn't limited to those times. If this becomes a recurrent issue, see your doctor.