The absence of distinctive facial markings, and the diagonally projecting cats-whiskers by the head, suggest Lasiocampidae, although it does not resemble the photos of any of the 20 species caterpillars illustrated at http://lepidoptera.butterflyhouse.com.au/lasi/lasi-cats.html so it is probably one of the other 56 unillustrated named Australian species in that family. I do hope you have it in protective custody and can rear it to the adult moth which will be easier to identify.