Buy in May and be prepared to stay: Pro

Forgot the old saying "sell in May and go away" — this is the year to "buy in May, but be prepared to stay," said Kevin Mahn, president and chief investment officer at Hennion and Walsh Asset Management.

A day after hitting an all-time high Thursday, the S&P 500 set another intraday high Friday. The Nasdaq 100 reached its highest level in over 13 years.

"We are in the midst of a secular bull market," Mahn said, noting that secular bull markets have an average length of 14 years. "We're only 4 years into this one."

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While Mahn sees more upside in the second half of 2014, he thinks there will be more potential in the international markets than domestic.

However, "so long as you find companies that are growing their earnings [and] trading at a reasonable price, I still think there's room for growth in this market," he told CNBC's "Power Lunch."

A trader works on the floor of the New York Stock Exchange.
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A trader works on the floor of the New York Stock Exchange.

Burns McKinney, portfolio manager at NFJ Investment Group, agrees that "there are probably cheaper opportunities outside the United States."

However, he still expects stocks to rise in the U.S.— but has one note of caution for investors.

"There's been a heavy correlation between the size of the central bank's balance sheet and equities over the last 5 years," McKinney said.

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With the Federal Reserve's tapering, he expects stocks to rise at a more gradual rate going forward the rest of the year.

And it's not only the U.S. central bank that's having an effect on the market, he said. The expectations for a European Central Bank rate cut are also affecting U.S. bonds.

"More likely than not, a lot of the reason for the decline in U.S. rates has just simply been that you have lower rates elsewhere in the world, so you just have an upswell in demand from investors elsewhere," McKinney said.

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—By CNBC's Michelle Fox