Could be your heart rate just tends to be on the high side. If you don't have any discomfort or trouble breathing and you are able to return to a normal resting heart rate within a reasonable amount of time after stopping, I would guess it's probably not a big deal. My doctor gave me similar advice a few weeks ago after I asked him why my resting heart rate seems high even though I'm in pretty good shape.
Plus - I don't take my max heart rate regularly now, but I remember doing so when I was a runner in high school and it was consistently on the high side. That 220-age formula never worked for me.