U.N. High Commissioner for Human Rights Navi Pillay said some of those arrested and charged with treason, from the International Socialist Organisation and other social justice and human rights groups, had alleged they were beaten in detention.
"The arrests appear to be part of a growing crackdown on civil society and members of the political opposition, and are a clear sign that the establishment of a consolidated democracy in Zimbabwe is still very far from assured," she said in a statement .
Police in Zimbabwe said they arrested 46 people in Harare last month as they watched videos of North African protests and discussed possible demonstrations in Zimbabwe, where President Robert Mugabe, 87, has held power for 31 years.
Pillay, a former United Nations war crimes judge, has spoken out in support of protesters in North Africa and the Middle East and said a crackdown against demonstrators in Libya could amount to crimes against humanity.
She said on Tuesday the uprisings had made it clear "there is no true democracy without freedom of expression and assembly".
"It is therefore both deeply ironic and disturbing that, in Zimbabwe, activists are being arrested and mistreated simply for discussing North Africans’ efforts to bring about change through largely peaceful protests," she said.
Calls via social media websites for protests on Tuesday against Mugabe’s 31-year-old rule did not lead to mass gatherings in Zimbabwe, where police have threatened to crush "Egypt-style" protests.
The campaigns on Facebook and Twitter were aimed at starting popular uprisings similar to those that toppled the presidents of Tunisia and Egypt and are threatening Libyan leader Muammar Gaddafi.