"Saudi authorities have arrested over 160 peaceful dissidents in violation of international human rights law since February 2011," HRW said in a statement.
It called on "the interior minister, Prince Nayef bin Abdul Aziz al-Saud, to order the immediate release of peaceful dissidents, including Nadhir al-Majid, a writer and teacher arrested on April 17."
Most of the arrests were in Eastern Province, where the Shiite minority has been holding protests calling for political reforms and the release of prisoners.
HRW slammed Saudi Arabia's western allies, especially the European Union and the United States, for not taking a harder line over the conservative Gulf kingdom's arrest of dissidents.
"As the list of Saudi political prisoners grows longer, the silence of the US and the EU becomes more deafening," Christoph Wilcke, a senior Middle East researcher at HRW, said in the statement.