Armed police took away Jestina Mukoko and eight activists to a maximum security prison on Thursday, defying a High Court order for their immediate release to a local hospital.
They have been charged with recruiting or trying to recruit people, including a police officer, to overthrow Mugabe’s government.
"They (police) are saying they have not seen the order and so they are not in a position to release them," Alec Muchadehama, a lawyer for Mukoko and the activists, told Reuters.
"We are in the process of serving more police officials with the order so that they have no more excuses. They will have to come up with another reason for refusing to release them."
The police could not be reached for a comment.
High Court Judge Yunus Omarjee ordered the release of Mukoko, the co-accused, and 23 other activists because their detention was illegal.
Lawyers complain that Zimbabwean police often delay or refuse to carry out court orders especially when it involves Mugabe’s opponents.
There were allegations that Mukoko and her eight co-accused had been tortured, and they were supposed to be taken to hospital for treatment after the court ordered their release.
The case raised new doubts about the implementation of a power-sharing agreement between Mugabe and opposition leader Morgan Tsvangirai, seen as a chance of rescuing the once relatively prosperous country from economic meltdown.
Negotiations are deadlocked over key cabinet posts, pushing Zimbabwe deeper into crisis.
Tsvangirai has threatened to suspend negotiations on the September 15 power-sharing agreement if arrests do not stop. His party accuses the government of abducting its members to force Tsvangirai into a co-operative government.
Mukoko’s independent organisation monitored human rights and had compiled reports of violence at this year’s elections.