MarketWatch chief economist Irwin Kellner says retail investors are showing strong skepticism about the stock rally, indicating they may be ready to sell.

Major stock indices are at or near record highs, with the Standard & Poor's 500 Index up 29 percent so far this year.

"Some investors are beginning to worry that a correction may be nigh," Kellner writes on MarketWatch.

Editor’s Note: 5 Reasons Stocks Will Collapse . . .

"When I tell people that stocks are trading on corporate profits, their response is how much longer can business make money if consumers’ buying power is so poor and unemployment is so high?"

When he cites Federal Reserve easing as supportive for stocks, "their reaction is that the Fed is reportedly ready to take the punch bowl away by reducing the amount of money it is injecting into the bond markets."

Investors also are worried about Washington's political gridlock, Kellner says.

"None of these issues is conducive to getting a good night’s sleep," he writes. "So don’t be surprised if it’s the small investor who bails out first, leaving the big institutional investors holding the bag, instead of the other way around."

While stock market guru Jeremy Siegel of the University of Pennsylvania sees a possibility for a correction soon, the market's underlying path is higher, he tells CNBC.

"My data shows that the fair market value based on current [projections of future] earnings for the Dow [Jones Industrial Average] is probably around 18,000." That would represent a 12 percent gain over Tuesday's close of 16,073.

Editor’s Note: 5 Reasons Stocks Will Collapse . . .

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