The inflows marked the strongest demand for the low-risk funds in six weeks. Investors are growing cautious toward the U.S. stock market after record highs this year, said Tom Roseen, head of research services at Lipper.

Investors are "sitting back, waiting, maybe even taking some profits," Roseen said. "They're very concerned."

The Standard & Poor's 500 stock index has risen 25.2 percent this year.

Investors still committed $1.5 billion to stock funds over the weekly reporting period that ended Wednesday, marking the fourth straight week of inflows into the funds.

The S&P 500 fell 0.8 percent over the reporting period, however, on conflicting data on the strength of the U.S. economy. The data has fueled uncertainty over when the Federal Reserve would scale back its $85 billion in monthly bond-buying.

While U.S. private-sector job growth was strong in November, weaker-than expected data on service-sector growth led some strategists to believe that the central bank would hold off until the economy is on firmer ground.

Taxable bond funds had outflows of $258 million, reversing inflows of $141.5 million over the previous week.

Funds that hold high-yield junk bonds had outflows of $141.4 million, marking their first withdrawals in four weeks.

Investors are anticipating that bond interest rates will spike higher once the Fed pulls back its monthly bond-buying stimulus, Roseen said. The Fed meets later this month.