Hi happy John,
It all depends where you are and where you are planning to go.
In Victoria there are three online sources go info that I know of.
1. VicRoads website will have info about main roads and highways but will usually have nothing about the bush tracks.
2. Parks Victoria website will have info about closures of parks, campground and tracks within parks and
3. DEPI / DELWP have an online map based system called the Public Access Map. This shows current and planned closures due to seasonal closures, track conditions and road works but doesn't always show closures due to relatively short term things like fires and planned burns, but common sense would suggest that there are temporary closures in place around any fire or burn. The Public Access Map is not easy to find but it is there! And they are called Department of Environment Land Water and Planning these days.
Additionally you could get info from 4wd Victoria as they get involved with the yearly seasonal closures. These are usually in place over the wetter months and most are in place from after Queens Birthday weekend to before cup day weekend.
Hope any of this helps.