Australian Federal Police Assistant Commissioner Neil Gaughan said 180 police took part in the raids on nine properties in the east coast cities of Brisbane and neighbouring Logan.
The raids came hours after Australian Security Intelligence Organization Director-General David Irvine warned that Australia's terrorist threat level could be lifted from "medium" to "high" this week because of the growing danger posed by Islamic State group supporters.
A police spokesman could not immediately explain whether the allegations were that they were preparing themselves or others to fight.
The 21-year-old is also charged with recruiting persons to engage in hostile activities in Syria. The 31-year-old has also been charged with providing funds to Jabhat al-Nusra.
"There is no information or intelligence available to police or security agencies at this time to indicate that that these males were involved in terrorism attack planning in Australia," Gaughan told reporters, adding that the arrests and raids were the culmination of a yearlong investigation.
Police seized a "significant amount of electronic data," a firearm and some crossbows in the raids, Gaughan said.
Irvine told the National Press Club last month that an estimated 60 Australian citizens were fighting for Jabhat al-Nursa, also known as the Nusra Front, and another al-Qaida offshoot, the Islamic State group, in Iraq and Syria. Another 15 Australian fighters had been killed, including two young suicide bombers.
Queensland Assistant Police Commissioner Gayle Hogan said there was no threat to the G-20 meeting.
