Google plans to use the acquisition to extend its internet advertising business to mobile devices.
The US Federal Trade Commission (FTC) is questioning Google's competitors and advertisers over monopoly concerns.
But Eric Schmidt, chief executive at Google, said in a US television interview that the mobile advertising space is "hugely competitive" with up to seven companies vying for a share of the market.
Google believes this is an acquisition that should go through, and if it does not, we will fight about it, he said.
The FTC is expected to make a ruling on the deal soon after a delay to prioritise an investigation into the effects of Apple buying Quattro Wireless in January.