Billionaire investor Warren Buffett said Thursday there's no question a basket of U.S. stocks will do better over time than bonds.

Stocks are "considerably more attractive," Buffett said in an interview with CNBC's Becky Quick on "Squawk Alley." "Over time, a bunch of businesses that are earning higher returns on capital are going to beat a bond that's fixed at roughly 3 percent."

When he asked whether he's buying stocks, Buffett said, "We're buying stock this morning."

Buffett, also known as "The Oracle of Omaha," said he's bought stocks under every U.S. president. He added the reason stocks are worth "a whole lot more" than decades ago is because American corporations have "plowed back part of the earnings."

Buffett continued, "You can [also] buy a duplex next door and rent it out to people and do fine over time or you can buy a small piece of farm land or something or you can put it into something fixed income — bonds, bank deposits."

Watch the full Buffett interview here.

Earlier this month, a regulatory filing revealed that Buffett's Berkshire Hathaway increased its stake in Apple by 5 percent during the second quarter of this year.

The conglomerate also upped its holdings in Goldman Sachs, Delta Air Lines, Southwest Airlines and Teva.

The chairman and CEO of Berkshire Hathaway, who turned 88 Thursday, joined CNBC from the Smith & Wollensky steakhouse in New York, where he was to have lunch with the winning bidder of the annual Glide charity auction.

The anonymous bidder paid more than $3.3 million to have lunch with Buffett. The proceeds of the auction benefit Glide, an anti-poverty organization in San Francisco that Buffett became involved with through his late first wife, Susan.