Last week, Google announced a partnership with mobile giant Verizon (VZ) Wireless to market Android-equipped smartphones that will compete against Apple's iPhone.

In a statement, Google made no mention of the FTC probe, and CEO Eric Schmidt described Levinson as a good friend and valued colleague. "Art has been a key part of Google's success these past five years, offering unvarnished advice and vital counsel on every big issue and opportunity Google has faced," Schmidt said. "Though he leaves as a member of our Board, Art will always have a special place at Google."

Levinson, who has served on Google's board of directors since the company's IPO in 2004, made similarly boring comments. "Working with Eric, Larry, Sergey and the whole Google team has been a remarkable experience for me. I greatly admire what they've built and have no doubt that Google has a terrific future," Levinson said in the statement.

Levinson's resignation from Google's board comes as both the seach giant and Apple are preparing to report quarterly earnings -- Google this Thursday, and Apple next Monday. A Google spokesman did not immediately return a request for additional comment.