They are accused of setting fire to a number of vehicles, including police vehicles.
But vocational students at the fire scene near Orathai bridge told the Bangkok Post these people had not played a role in setting the fires.
They also claimed they had seen the arrested suspects physically assaulted by police.
They asked police to look into the case fairly.
Rommadon Sukploy, a senior vocational student, said no students could get out of the Rajamangala University of Technology Phra Nakhon because police had fired heavy amounts of tear gas and sprayed water into the university.
Mr Rommadon said some vocational students had been attacked with glass balls and knotted ropes.
"We had only firecrackers, pingpong bombs and sticks," Mr Rommadon said.
"We didn't have any petrol that was used to start the fires."
A vocational student said he had seen a black-clad man emerge from the police lines and set fire to the police vehicles.
Damaged in the attacks were cars belonging to the police and the Bangkok Metropolitan Administration.
A pickup truck parked at the bridge was also damaged in the attacks carried out on Monday night, deputy police chief Pol Gen Worapong Chiewpreecha said.
A preliminary police investigation showed the seven suspects were vocational students taking part in the anti-government protest, he said, adding that they were detained at Wat Sommanat.
Along with the arrests of the seven people, police also seized bottles containing petrol, stones, plastic bags containing petrol, giant firecrackers attached to petrol bottles and bags of alcohol, shotgun shells, .38-calibre bullets, large electric fans, chopping knives, golf clubs, clay balls with spikes, and whistles.
These weapons were allegedly found hidden in an unidentified four-storey commercial building near Government House.
Pol Gen Worapong said police had information the suspects were normally at Chamai Maruchet bridge when rallying and they might be linked to the deadly violence that occurred on Sunday at Ramkhamhaeng University.
City police chief Pol Lt Gen Khamronwit Thoopkrajang, who is responsible for the police's handling of the street protests, said weapons were used in an attack at Orathai bridge on Monday night which resulted in a number of police officers getting shot.
Meanwhile, a police bomb disposal team took about five minutes to retrieve an object looking similar to a grenade that had already been unpinned.
The object, which turned out to be an inert grenade that is normally used for throwing practice by the military or police, was found dropped in Khlong Phadung Krung Kasem.
Bangkok Metropolitan Administration spokeswoman Treedao Apaiwong said a burned water tanker at the scene did not belong to City Hall.