"In all the cases documented, the activists were acquitted or the state abandoned the cases, or the cases are pending," the report said.
Mugabe's government should use the new constitution as "a golden opportunity" to improve its poor human rights record and allow for freedom of expression, said Noel Kututwa, Amnesty's deputy director for southern Africa.
"The new Constitution offers a golden opportunity for the government to begin to right the wrongs of the past, to deliver justice for its people and to allow freedom of expression. With political will, all that is possible," Kututwa said.
Following Mugabe's re-election in the disputed polls in July, police continued to breach the new constitution by breaking up a demonstration by women activists and banning a youth march to mark World Peace Day in September.
Baton-flailing police in Harare dispersed activists from Women of Zimbabwe Arise, or WOZA, who were calling for action to improve living standards for Zimbabwe's poorest. Several members of the group were arrested for questioning in the second city of Bulawayo.
The police defended their actions describing the country's current political environment as not "conducive" for marches.
Kututwa said Mugabe's new government should send "a clear signal" that it will end rights violations.
"The rights to freedom of expression and association of all those working to promote or protect human rights must be respected," he said. "The government must immediately and unconditionally drop the charges against anyone arrested for exercising their internationally guaranteed rights."