A BlackRock Inc. BLK -0.33% investment fund is leading the deal, which also includes previous backers, said one of these people, who declined to provide more detail.
Dropbox wasn't immediately available to comment.
At $10 billion, Dropbox is one of the most highly valued companies backed by venture capitalists. The company's valuation has more than doubled since late 2011, when investors valued the San Francisco-based company at $4 billion. The company also got a higher price than expected when it approached investors as recently as November.
Dropbox raised $250 million in its 2011 financing from Goldman Sachs and venture-capital firms including Sequoia Capital, Index Ventures and Accel Partners.
The Wall Street Journal previously reported that Dropbox had expected sales of more than $200 million in 2013. The company made $116 million in sales in 2012, according to people familiar with the company's financials, more than doubling its $46 million in revenue in 2011. The year before, it nearly quadrupled sales from $12 million.
--David Benoit contributed to this article.