Zhang Xiangzhong, an activist associated with the New Citizens Movement, whose members held small-scale protests calling for government officials to disclose their assets as a curb against graft, stood trial on a charge of "credit card fraud", his attorney Xie Yanyi told AFP.
Beijing does not tolerate organised dissent and has cracked down on members of the loose-knit group, detaining dozens and sentencing several to prison.
"He has been targeted because of his involvement in the protests over asset disclosure," Xie said, arguing that the evidence was insufficient and Zhang had pleaded not guilty.
Xie said that police surrounding the court, in the city's northwestern Haidian district, denied access to those hoping to attend.
"It's effectively a secret trial... and in the view of the lawyers, it's totally illegal," he said.
Representatives from around 10 foreign countries attempted to observe the trial but were denied access, a European diplomat said, adding that there was a heavy police presence around the court.
New Citizens Movement members argued that asset disclosure would help curb rampant corruption in China, as President Xi Jinping has pledged to root out official graft.
Beijing's high court in April upheld a four-year jail sentence for Xu Zhiyong, a founder of the movement.
The verdict was condemned by international rights groups as well as the United States and European Union.
Members have said the wave of arrests, which began last year, have heavily curtailed their activities.
At its peak the group had an estimated several hundred participants, who organised dinner discussions across the country and pushed for legal and educational reforms.
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