"Android has a patent fee," said Ballmer, in an interview published Monday in The Wall Street Journal.
"It's not like Android is free. You do have to license patents. HTC has signed a license with us and you're going to see license fees clearly from Android as well as for Windows," said Ballmer.
Ballmer may have been making a veiled reference to the fact that his company claims to control patents that govern technology behind many open source software products—and that it's not afraid to use the courts to determine the legitimacy of those patents.
Last week, Microsoft disclosed that it was suing Android handset maker Motorola for patent violations. The question now is whether Microsoft will go after Google itself over what it might claim are Microsoft patents embedded in Android.
All of this comes as Microsoft prepares to launch Windows Phone 7, which many analysts believe represents the company's last chance to establish itself as a player in the smartphone market. The company will formally introduce the mobile OS platform on Oct. 11, at a launch event in New York City.
Windows Phone 7 devices, from a list of Microsoft partners that includes HP, Samsung, LG, Toshiba, and Sony Ericcson, are expect to go on sale about a month later. AT&T and T-Mobile will reportedly be the U.S. network carriers.
RIM, with its Blackberry OS, holds the largest U.S. market share for mobile platforms, with a 39.3% stake as of July 30, according to market watcher Comscore. Apple's iPhone is second, with a 23.8% share, followed by Google's 17% share. Microsoft was fourth, with an 11.8% stake.