Human Rights Watch said Friday's emergency court trial of Ashraf Ibrahim and four other political dissidents is an attack on basic freedoms.
Ibrahim has been in detention since 19 April on charges of "sending false information" to human rights organisations abroad, and of membership of a "revolutionary socialist group".
His arrest is widely believed to be linked to his monitoring of police brutality against anti-war demonstrators in March.
The other defendants are Nasr Farouq al-Bahiri, Yahya Fikri Amin Zahra, Mustafa Muhammad al-Basiuni, and Rimon Edward Gindi Morgan.
'Travesty of justice'
They also face charges of membership of a banned subversive group, but have not as yet been taken into custody.
"A court that denies the basic right to a fair trial and indictments that criminalise free speech and freedom of association can only produce a travesty of justice"
Human Rights Watch
"A court that denies the basic right to a fair trial and indictments that criminalise free speech and freedom of association can only produce a travesty of justice," said Joe Stork, acting executive director of Human Rights Watch's Middle East and North Africa Division.
"If President Mubarak's talk of democratic reform meant anything, the government would halt these proceedings immediately and release Ashraf Ibrahim from detention."
He added: "If the state has evidence of criminal wrongdoing against any of these defendants, it should bring charges that meet international standards.
"And it should make sure they go before a competent and impartial court of law."
Ibrahim turned himself in to the authorities on 19 April, after
police raided his home and seized his personal computer, camera and documents.
He was detained without charge in Mahkoum Tora Prison, outside Cairo, for four months.
On 7 August, the High State Security Prosecution charged him and the other four defendants with membership of a banned subversive group.
The indictment also accused Ibrahim of intentionally "sending
are banned in Egypt
false information to foreign bodies - foreign human rights
organisations - which include, contrary to the truth, violations of human rights within the country."
Ibrahim was instrumental in exposing police brutality during an anti-war demonstartion in Cairo in March.
Rights groups condemned Egypt for using excessive force to disperse demonstrators protesting against the US-led war on Iraq.
HRW said after arresting hundreds of protesters, police beat and mistreated many detainees, some to the point of torture.
Most of the 800 people arrested were released within 24 hours, but 61 were held for investigation and charged with destruction of property, promoting disorder and other offenses.