Billionaire investor Warren Buffett defended some of his core holdings in a televised interview on Monday, but reiterated that equities in general would look expensive in an environment with normal interest rates.

The remarks from Buffett, chairman of Berkshire Hathaway (BRKa.N), come as several of his core holdings, including International Business Machines Corp (IBM.N) and Coca-Cola (KO.N), have showed declining revenue trends in recent years and their market positions aren't as impenetrable as they once were, amid increased competition.

Buffett told CNBC that Berkshire had bought more shares of IBM during the first quarter, and forecast higher earnings at the company over the next 10 years.

He also praised IBM's stock buyback program, which he said had been "enormously beneficial" for shareholders, though he stressed that in general, buyback programs should be done based on share price and not as an all-purpose strategy.

Coca-Cola continues to have a "strong competitive position," he said.

Referring to the broader market, Buffett said equity valuation would appear "on the high side" if interest rates were normalized from their currently low levels, repeating comments he had made over the weekend at the annual Berkshire Hathaway meeting.

While he acknowledged that investors expect interest rates to rise this year, he said it would be difficult for the United States to raise rates "significantly" if European rates remained low.

U.S. bonds, meanwhile, were "very overvalued," he said.