In an interview with talk show host Charlie Rose that aired Friday, Buffett said, "We've, net, bought $12 billion of common stocks since the election."
Buffett added it was "in large part" his decision.
The Omaha, Nebraska-based conglomerate owned $102.5 billion of equities as of Sept. 30, excluding its stake in Kraft Heinz, according to a regulatory filing.
Stocks and Treasury yields jumped in the wake of Trump's victory, amid the prospects for looser regulations in certain sectors, lower tax rates and fiscal stimulus. The rally has waned recently as investors evaluated the president's executive order that barred entry of certain nationals into the U.S.
Buffett was also skeptical that Trump could reach 4 percent annual growth.
Berkshire could disclose by Feb. 14 some of the stocks it has bought, in a regulatory filing listing of most of its U.S. holdings as of year-end.