"Currently there are still all kinds of movements such as secret meetings that have made us more cautious," he said.
Earlier this month Thailand extended the ban on public gathering across one quarter of the country, prompting concern among rights groups and key allies including the United States.
The decree was applied after two months of mass Red Shirt rallies, which pushed for fresh elections, spilled into violent clashes with Thai security forces that left at least 90 people dead and nearly 1,900 others injured.
The demonstrations ended in May following a heavy military crackdown on the protesters, who were broadly supporters of Thaksin Shinawatra, the expelled former Thai premier.
Puea Thai, the country's main opposition party, dismissed the move to end emergency rule in three provinces as insufficient, saying the authorities were simply trying to gain favour from voters.
"The government must lift emergency rule in all 19 provinces, especially Bangkok, where there will be an election this weekend and our campaign is restricted under this law," Pormpong Nopparit, a spokesman for Puea Thai, said.
The authorities have used the emergency state to arrest hundreds of suspected violators, including most of the top leaders of the Red Shirt movement.
They have also shut down anti-government TV channels, radio stations and websites.
US-based group Human Rights Watch said earlier this month the government was "systematically using" the emergency decree to hold suspects without charge for up to 30 days in unofficial places of detention.
Many detainees have been held at military camps but their exact numbers and whereabouts are unknown to their families, it said.