When an economy is temporarily operating at an output that is beyond its full-employment rate it means that

It means that excess demand in resource markets will lead to higher resource prices, which will increase costs and direct the economy toward full employment.

Explanation:

An economy's full employment output is the highest production level when all available resources are used efficiently. It equals the highest level of production an economy can sustain for the long-run. It is also referred to as the full employment production which results in long term supply of the finished good.

When there is increased demand then eventually there will be an increase in the price and also costs of the production which leads the economy towards the full employment output as it is a sustainable output.