"As soon as the vote is over, the focus will be on fundamentals, and I think there's a mixed picture. On a value basis, you look at some of the big German companies that have a dividend yield that's two or three times what it cost them to issue debt, so it would almost appear to be an arbitrage opportunity," Keon said.
"At the same time, there is still fairly weak growth. In the United States we did get a disappointing labor report the last time, so I think we're probably going to continue to work our way higher over time, but I don't necessarily think that there'll be a large positive reaction as a result of a remain vote, if that were to occur," he said.
Financial markets across the globe were also expecting the U.K. to stay in the EU. U.S. futures spiked, while the British pound continued surging against the dollar, hitting its highest level since Dec. 25.
"There is a risk that the referendum, ironically, despite the big buildup, now becomes a bit anticlimactic," Marc Chandler, global head of currency strategy at Brown Brothers Harriman, said on "Squawk Box." "About a week ago, … we were trading about $1.4010 in the British pound, now we're at $1.49."
GBP/USD since June 15Source: FactSet
Tim Edwards, senior director of index investment strategy at S&P Dow Jones, said markets are also partially pricing in the possibility of a Brexit.
"We had thunderstorms and lightning last night and it's a very nervous day in London. Whatever happens, there will be some movement in price. Even though the market has called for, or is pricing for, remain, [it] is still pricing some possibility … of a Brexit," he said.
— CNBC's Gina Francolla and Reuters contributed to this report.