If you otherwise feel fine when your heart is beating faster than normal, it's very unlikely to be dangerous. However, it should be always be temporary — perhaps related to anxiety, stress, excessive caffeine intake, use of non-prescription decongestants or other types of medications, or dehydration. Drink some extra fluid, take ten minutes to relax, and consider whether anything you have been drinking or taking might be causing the fast heart rate.
If your heart rate persistently feels like it is too fast, you might have an overactive thyroid gland. Less likely but still possible is that you do have an abnormality of the electrical system of your heart.
Call your doctor's office for advice. Call immediately if you begin to feel lightheaded or faint.