T. Rowe Price joined the growing ranks of mutual fund companies seeking to enter the nascent market for actively managed exchange-traded funds when it applied to the Securities and Exchange Commission for approval to start a family of these vehicles.

The big Baltimore-based mutual fund complex follows other active managers like Pimco, Vanguard, Black Rock's iShares and start-up venture Grail Advisors in looking to expand the ETF market, traditionally dominated by passive index ETFs, into the actively managed arena. So far, actively managed ETFs have not attracted large asset flows, but the vehicles are so new that the jury is still out.

The SEC filing indicates T. Rowe's family of ETFs will initially focus on the domestic and international equity markets as well as the fixed-income business.