As the S&P 500 and the touched new highs, the bull market still has room to run, Josh Brown of Ritholtz Wealth Management said Monday.

"I think the thing to think about here is, no one can really look at this market and say it's cheap, but since when do bull markets stop at cheap?" he said. "I can't think of a single example in modern history. We overshoot to the downside during despondency, and we overshoot to the upside during what they would call euphoria. I don't quite think we're at a euphoric high."

(Read more: US stocks end mostly lower; Dow below 16,000 on Icahn's bearish talk)

On CNBC's "Fast Money," Brown noted a historical perspective.

"Most bull markets end at 17.8 times earnings," he said. "We're about 15.5 times."

Brown also said that strength in stocks outside the United States supported a continued bull run.

"Global participation is obviously better than the massive bifurcation that we had had in prior rallies," he said.

(Read more: S&P 500 to hit 1,825 this year: JPMorgan's Tom Lee)

Brown said that he hoped the market wouldn't continue to climb in a straight line.

"I don't see why, unless you're a total pig, you need an up-3 percent month every single month in a row," he said. "I think it makes much more sense for us to digest. We hit some big, round numbers, like 1,800, Nasdaq 4,000, Dow 14,000."

Stuart Frankel's Steve Grasso said staying in the market is crucial.

"People have stayed invested, have been rewarded with this marketplace," he said. "And if you've gotten out, you've always made a bad sale."

—By CNBC's Bruno J. Navarro. Follow him on Twitter @Bruno_J_Navarro.