Mutual funds, including ones managed by giants BlackRock, Fidelity Investments and T. Rowe Price Group, are taking the plunge into venture capital in a big way.

The investments have included stakes in prominent technology companies such as Airbnb, Dropbox and Pinterest, The Wall Street Journal reports.

The investments could pan out big time if the companies are sold or go public, juicing the funds' performance. But the young technology companies also could easily flop, denting the companies' returns.

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"These are unproven companies that could very well fail," Todd Rosenbluth, director of mutual fund research at S&P Capital IQ, tells The Journal. If a startup company flounders, "there may not be an exit strategy" for the mutual funds investing in it, he said.

BlackRock, T. Rowe, Fidelity and Janus Capital Group bought into a combined 16 private funding deals last year, up from nine in 2012, according to CB Insights, a venture-capital research firm, The Journal reports.

In 2014, the four firms already have participated in 13 deals. T. Rowe participated in a $450 million investment round for Airbnb last week, knowledgeable sources tell The Journal.

Meanwhile, venture capital activity in general is soaring, leading some analysts to question whether the tech sector is in another bubble.

Venture capital investments totaled $9.5 billion in 951 U.S. start-ups in the first quarter, up 57 percent from a year earlier, according to a report from PricewaterhouseCoopers, the National Venture Capital Assn. and Thomson Reuters.

That's the largest amount since the second quarter of 2001, according to the Los Angeles Times.

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