The Federal Trade Commission is investigating Google Inc. (NASDAQ:GOOG) for their acquisition of AdMob.  The FTC is checking to see if the acquisition of AdMob would reduce competition for advertising on mobile phones.

“We’re not going to discuss the details of that process,” stated Google spokesman Adam Kovacevich. “We’re confident that they’ll conclude that the rapidly growing mobile advertising space will remain highly competitive after this deal closes.”

A combination of Google and AdMob would create the largest mobile advertising company.  The companies controlled about 21% of the market combined in 2009. [Bloomberg]