The stock market has been hitting new highs this year as excitement continues to build with respect to artificial intelligence (AI) and the opportunities that may open up for many businesses. Should investors take Buffett's conservatism in the markets this year as a red flag?

Warren Buffett is the CEO of Berkshire Hathaway ( BRK.A 0.99%) ( BRK.B 0.95%), which has delivered an annual return of 19.8% since Buffett took the helm in 1965. That could have turned an investment of $1,000 into more than $42 million. The same investment in the S&P 500 index would have grown to just $308,115 over the same period.

Warren Buffett continued to sell Apple during the third quarter, but that wasn't his most surprising move -- not by a long shot.