From Aljazeera:

Australia has raised its terror threat level to “high” from “medium”, saying there is an increased likelihood of an attack at home, despite stressing it has no knowledge of a specific plan.

Australia has repeatedly raised the alarm about the number of its citizens believed to be fighting with armed groups in the Middle East, including a suicide bomber who killed three people in the Iraqi capital Baghdad in July and two men shown in images on social media holding the severed heads of Syrian soldiers.

This comes on the heels of Britain raising the their threat level, but the US has not done the same.