Dealer will take care of it. Also popped up for me last week, right after a "Check Gas Cap" readout. I pulled over, verified that gas cap was tight (turned one notch to right-that's it), and went on... No loss of power or anything. When I took her in for Inspection II this week, they said the Gas Cap error reflects a loss of fuel-line pressure, so the SES automatically clicks on. They checked the fuel lines, tanks and cleared the errors.
So it doesn't have to be too big a deal... and that's probably the case with your mileage. I'd take it in just to be sure, or code-read it to see what the initial cause was, if possible.
Hope it works out!
M