When he heard the news, Liu Xiaobo cried and said the Nobel "award is for the Tiananmen martyrs," according to the Washington-based group, which said it represents the Chinese dissident. The group works worldwide for the release prisoners of conscience and provides free legal counsel.
Freedom Now lawyer and spokeswoman Beth Schwanke said one of the group's human rights specialists, Yang Jianli, obtained news of Liu Xia's detention from a source in China they could not name over fears that the informant would also be detained.
"Liu Xia is under enormous pressure," said Jianli, who the group said is currently in Taiwan.
Liu Xiaobo won the Nobel Peace Prize on Friday for two decades of non-violent struggle over human rights, infuriating China, which called the award "an obscenity."
The prize shines a spotlight on human rights in China at a time when it is starting to play a leading role on the global stage as a result of its growing economic might.
Liu has been in and out of jail since 1989, when he joined student protesters on a hunger strike days before the army crushed the Tiananmen Square pro-democracy movement. He was jailed for 11 years in December for subversion of state power.
Liu Xia said on Friday she was being taken to visit her husband in jail but that police were preventing her from talking to reporters.