Warren Buffett, chairman and chief executive of conglomerate Berkshire Hathaway, said Monday he would be more likely to buy than sell IBM shares over the next two years, and that he did not seek to profit from global central bank actions.

Buffett, who presided over Berkshire's 51st annual shareholder meeting in Omaha, Nebraska over the weekend, told cable television network CNBC: "We would be much more likely to buy more in the next 12 or 24 months than we would be to sell shares, but we will make that call as time goes along."

Buffett, whose Berkshire held an 8.59 percent stake in IBM as of the end of last year and who has caught some flak for his stake, said his cost basis in IBM was around $170 a share and that he had still never sold a share.

IBM shares were little changed at $145.60 in morning trading Monday.

Buffett also said he did not seek to profit from global central bank monetary policies, but that low and negative interest rates could produce an unanticipated reaction.

"It's a fascinating movie to watch. I don't try to make money off the movie," Buffett said.

"If currency in a bank is worth less than currency in your hands or in a mattress, that could produce something in the way of behavior that nobody has ever anticipated."

Buffett, whose Berkshire is an American Express shareholder, said the company's loss of its contract with retailer Costco Wholesale Corp was "significant" but he agreed with American Express Chief Executive Kenneth Chenault's decision to split from Costco.

He said American Express would remain "under attack" from alternative payment methods, but he was confident in his stake.

"Costco was a very, very, very valuable co brand to have for American Express, but that value wasn't limitless," he said.

Berkshire Vice Chairman Charlie Munger told CNBC, however, that he would have made the opposite decision with regard to American Express's contract with Costco.

Buffett also criticized companies that repurchase their own shares at too high a price: "They have in mind a limit as to what they pay for any business they buy except their own, and it has become fashionable to repurchase shares."

Buffett, who has ordered that most of the money he is not giving away at his death should be placed in an index fund, also said active investing as a whole was "certain" to produce worse-than-average results.

Buffett and Munger added to previous criticisms they have made of embattled drugmaker Valeant Pharmaceuticals International Inc's drug-price hikes.

Buffett said there "really wasn't any defense" for Valeant's price hikes, while Munger said Valeant was "leading the pack" of certain industry players who were raising prices dramatically.

"I don't think you'd want your son to grow up and run a company in the manner that Valeant was run," Buffett said.

Munger said he suspected it was "massively stupid" for the U.S. government to rely heavily on printing money and lightly on fiscal stimulus for infrastructure, and that the United States would have been better off with more fiscal stimulus.