"These people had been under surveillance for quite some time - that's the reason their passports were cancelled because they had been under surveillance and their intentions to travel to the Middle East to engage in terrorist war fighting were known to the authorities," he told reporters today.
"When it became clear to them that they wouldn't be able to leave the country in an orthodox way, they remained under surveillance so that if they attempted to leave the country in this very unusual way they would be able to be stopped and they were."
Brandis said police had executed 10 search warrants in Melbourne and far north Queensland as part of their investigations.
He stressed that there was no current or impending threat of a terrorist act in Australia and the alert level remained at "probable", where it has been since September 2014.
However, a number of people remain under police surveillance and will be arrested if they attempt a terrorist crime or try to leave Australia to take part in terrorist attacks overseas, Brandis added.
"Obviously, at one level, there was an unusual character to the plot. I know it has been ridiculed," he said.
"But these are serious crimes because they involve preparation to engage in terrorist war fighting overseas, and that is against Australian law."
- AAP