Bill Gates participates in a media availability on agricultural research, Thursday, March 13, 201, on Capitol Hill in Washington. (AP Photo/Susan Walsh)

Bill Gates sounded a skeptical note about Facebook CEO Mark Zuckerberg's decision to pick up WhatsApp on ABC's “This Week" Sunday.

Gates seemed critical of the price Facebook paid for its recent acquisition. “Fifty years ago, no 55-person company was bought for $19 billion. And that’s a good thing,” he told host George Stephanopoulos.

As for what the acquisition suggests about Zuckerberg himself, Gates said, “It’s an example of how he’s an out-of-the-box thinker. He’s aggressive. I hope it works out for him. Not everybody would’ve done it, I’ll say that for sure.”

The Microsoft founder had earlier discussed the deal in an in-depth interview with Rolling Stone magazine "I think his aggressiveness is wise -- although the price is higher than I would have expected," Gates said. He called Zuckerberg "more of a product manager" than he ever was.

Besides the high price, the Facebook-WhatsApp deal has also been controversial because of the companies' opposing takes on privacy. WhatsApp, which boasts nearly a half-billion users, has prided itself on collecting as little information about those users as possible, while Facebook is notorious for invading its users' privacy.

"People need to differentiate us from companies like Yahoo! and Facebook that collect your data and have it sitting on their servers. We want to know as little about our users as possible," WhatsApp CEO Jan Koum said in a Wired interview before the acquisition.