The 58-year-old man's body was found in northern New South Wales (NSW) on Thursday, days after a fire ripped through the region.
Crews are still battling over 120 fires in NSW and Queensland, but locals in Western Australia have now been warned of extremely dangerous conditions.
Police charged a 16-year-old boy with deliberately starting a damaging fire.
The alleged arson had destroyed 14 homes around the town of Yeppoon, 650km (400 miles) north of Brisbane, Queensland Police said.
Fire chiefs have warned the worst of the summer is "still ahead of us", after expressing alarm at the scale and severity of the spring bushfires.
Prime Minister Scott Morrison has often avoided questions on whether climate change has contributed to the fires, in a response that has drawn wide criticism.
Since Friday, four people have died and at least 300 homes have been destroyed or damaged by fires in NSW.
Police said the latest victim was found in burnt-out bushland near Kempsey, 400km north of Sydney. He was yet to be identified.
The discovery follows the deaths of Vivian Chaplain, 69, Julie Fletcher, 63, and George Nole, whose age is unknown. They were found in separate locations in rural NSW.