(like well below 1mA)
The data sheet says:-
12mA when running at 8MHz and 3.5mA when running at 4MHz
There is also the USB / serial bridge chip, so that pushes it up to 20mA.
This however is way too low for a poly fuse. Those things are very slow to blow and only protect the supply from short circuits, they won't protect the arduino from things like drawing too much current from a pin, putting 12V into the voltage reference pin or trying to power the chip with greater than 5V. All of which are common beginner mistakes.