It could be a mistake. When your blood is drawn, the lab has to let the tube sit for awhile so it will clot, then put it in a centrifuge to "spin" all of the red cells to the bottom of the test tube so there will be nice clear serum to test. (There is usually a gel barrier in the tube that will separate the red cells from the serum.) However, if the tube sat around for too long before it was centrifuged, or if enough of your red cells were damaged during the blood draw itself, potassium could have leaked from the red cells into your serum, making your potassium come back falsely high. In other words, your red blood cells contain potassium, so the result could be made false by not separating them from the serum soon enough. It is a common problem, because everyone's blood takes a different amount of time to clot, so they can't all be centrifuged right away, and sometimes they don't get centrifuged for HOURS, if the lab is backed up.
If your potassium repeats high, then you either do have high potassium and need to find out why OR your doctor's office/lab is continuously letting blood samples sit around too long before processing them, resulting in a lot of false high potassiums. This is more likely the case if they don't have a centrifuge at your doctor's office, so they have to send all their samples to the laboratory "unspun."
Also, if your tests for kidney function were normal (BUN/Creatinine), it's less likely you actually have high potassium... if they are abnormally high as well, your high potassium is more likely to be a true result.
Good luck-- I would not worry about this result, just be sure to get redrawn right away if you haven't already.