On start up the computer checks a set of data. When the check can't be completed for some reason the odometer will start to blink. The next time you start the engine and the check is ok, the odometer will stop blinking.
You don't have to worry if this happens once a month or so. Only when it happens frequently (or doesn't stop
) you have a problem with your systems check and a visit to the dealership is the only cure.