Australia has been asked to join United States in carrying out the air strikes, and Australian Prime Minister Tony Abbott has strongly hinted they will co-operate.
Mr Brownlee said there had been no similar request from US to New Zealand, nor was one expected.
Mr Brownlee said expanding New Zealand's role was not an option at this stage.
Australia was already involved in bombing IS targets in Iraq, but its aerial role in Syria had so far been limited to refuelling and intelligence-gathering.
US formally asked Australia to expand its air warfare role over Syria, and Mr Abbott said the government would carefully consider the request and make a decision in the next couple of weeks.
New Zealand and Australia were both involved in training troops in neighbouring Iraq.