Since January 20, the government has rounded up 114 journalists in a crackdown aimed at stifling protests against the king, the Paris-based group said.
Most have been released, but seven still remain behind bars and should be freed immediately, it said.
"Whether they were arrested for their articles or for demonstrating for press freedom, their detention is abusive," the statement said.
King Gyanendra took direct control of the impoverished Himalayan just over a year ago, sacking the government for failing to tame a decade-long Maoist insurgency and for alleged corruption.
Opposition parties boycotted controversial local polls called by the king on February 8.
The authorities this year have banned protests, imposed a curfew, cut mobile phones and rounded up hundreds of political activists and journalists.
The United States, India, Japan, Britain and the
European Union led a wave of international condemnation of the detentions.
The United said some 800 people were detained nationwide. Many have been released but scores remain behind bars, local human rights groups say.
Reporters Without Borders did not list the number of journalists being held in other countries.