Ballmer, who was speaking at Australian telecoms company Telstra's annual investment day, expressed disbelief at Google's business practices.
He said: "I don't really understand their strategy. Maybe somebody else does. If I went to my shareholder meeting, my analyst meeting, and said 'hey, we've just launched a new product that has no revenue model'... I'm not sure that my investors would take that very well.
Google's Android operating system is capable of running on many handsets, similar to Windows Mobile, except it is open-source, meaning anyone can develop for it.
Android will run Google's wide range of web applications such as Google Maps, Gmail and Google's newest brainchild, the Chrome browser.
Ballmer said: "They can hire smart guys, hire smart people, blah-de-blah-de-blah... but, you know, they start out way behind in a certain sense."
He reeled off a list of competitors in the mobile operating system market, such as Apple, Symbian, Blackberry and Mobile Linux, and said: "Google doesn't exactly bubble to the top of the list... They might some day. But right now..."
Ballmer's comments were part of a series of candid responses he gave attendees during a question and answer session at the Sydney event.
Google recently launched Android on the T-Mobile G1 handset. It hit UK shelves late October.
The G1 features a large format screen, much like the iPhone, a slide-out "Qwerty" keyboard and camera, and 24/7 automatic internet access.
Different handsets featuring Android will be released by various manufacturers around the world in the future.
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