The Taiwanese-flagged vessel, Ching Fong Hwa 168, with two Taiwanese and 14 Chinese crew members was captured in mid-May off the coast of the troubled Horn of Africa country.
"The information we have is that the pirates have released the vessel," Andrew Mwangura, head of the Kenya chapter of the Seafarers' Assistance Programme, told reporters.
"It was not clear whether the owners of the ship paid ransom as the pirates had demanded," explained Mwangura, who monitors shipping in the Indian Ocean and adjoining regions.
The US Navy confirmed the release of the the fishing vessel.
"It was released at 3.30pm. The pirates got off the vessel and the US Navy team went on board and offered them assistance they needed," said Commander Lydia Robertson, the spokesperson for US Naval Forces Central Command.
"It was escorted by the US Navy," Robertson told reporters.
In June, the pirates killed one crew member because the ship's owners failed to meet their ransom demands, officials said.
The release comes a day after pirates left two Tanzania-flagged vessels that had 24 Asian sailors onboard more than five months after seizing them. There are currently two pirated vessels still off the Somali waters.
Rampant piracy off Somalia's vast coastline stopped in the second half of 2006 during six months of strict rule by an Islamist movement that was ousted by Ethiopian and Somali government troops at the end of the year.
Somalia lies at the mouth of the Red Sea - on a major trade route between Asia and Europe via the Suez canal - and has lacked a functional government since the 1991 ousting of dictator Mohamed Siad Barre.