The Civil Court's ruling was sought by Thaworn Senneam, a PDRC core member.
He petitioned the court to order caretaker Prime Minister Yingluck Shinawatra, CMPO director and caretaker Labour Minister Chalerm Yubamrung and CMPO deputy director and police chief Adul Saengsingkaew to lift the emergency decree imposed in Bangkok, Nonthaburi and parts of Pathum Thani and Samut Prakan provinces.
The court in its ruling said Mr Thaworn had the right to file the petition with the Civil Court.
However, the government also had the authority to impose the emergency decree, a special law enabling the administrative branch to resolve problems during a critical situation, but with discretion.
However, the court prohibited the government and the CMPO from breaking up the People's Democratic Reform Committee's rallies and from seizing the protesters' equipment.
It cited an earlier ruling by the Constitution Court that the PDRC's rally is lawful as long as it is peaceful and without weapons.