The NSW Joint Counter Terrorism Team carried out raids in Sydney's southwest.
"Searches are still under way at Bass Hill, Merrylands, Swansea Park and Miller and at this stage we don't know the outcomes of those searches," Deputy Commissioner Catherine Burn told reporters.
The arrested teenager wanted to engage in hostile activities overseas but was stopped from leaving the country, Burn said.
People who travelled to either Syria or Iraq - or some other place where there are hostile activities - are more susceptible to carrying out violent acts back home, she said.