Only if you exceed your checked baggage allowance. Assuming travel from the US to Australia, the limit is based on the number of checked bags, and your class of service and/or OneWorld elite status. These limts are clearly outlines on the
Qantas Web site. For FF allowances,
see here.
Note that each checked item cannot exceed 32Kg. If you have elite status with OneWorld, they are more likely to waive any fee for excess baggage, but that will depend on how good/bad a day the particular agent has had.