A head of one of the largest U.S. private equity companies said a geopolitical surprise is the only thing for markets to worry about in the next two years.

"The only thing we have to worry about I think in 2018 and 2019 is some unanticipated geopolitical event, the so-called black swan," David Rubenstein, co-CEO of The , said Tuesday at CNBC's Net/Net dinner in Washington, D.C. He pointed to a possible North Korea missile launch or an event similar to the Sept. 11 attacks.

"But right now, short of those kind of things, I think the economy's in reasonably good shape and probably going to be spurred on a little by the tax bill," he said. Rubenstein said the tax bill should have "very favorable consequences for the economy" and he doesn't see any negative surprises from inflation or the labor market.