Windows have been smashed at the block of flats in Lampeter where a convicted sex offender is living.
An attack last weekend resulted in three windows being broken at the building, which is owned by a local housing association.
Dyfed-Powys Police have confirmed they are investigating an attack on a flat.
But they would not comment on claims the incident was linked to a particular case.
Residents believe vigilantes targeted the building because the unnamed sex offender lives there.
The man was bailed last week by magistrates after admitting taking photos of young children on Aberystwyth beach.
'Deplorable'
The residents say they are concerned that there will be further attacks.
Marje Harris said everyone living in the flats was nervous and she said the presence of the paedophile was "deplorable".
"Housing this man near a primary school is very insensitive and has upset people and affected them deeply.
"When I read in the paper that this man had been convicted of assaults, I was annoyed."
Reassurance
Another resident Shirley Hall said she was very nervous about going out.
"I went and saw the police on Monday because I wanted to know what they were doing. They said they had it in hand. There is CCTV across the road but it does not cover this area."
Lampeter deputy mayor Hag Harris said he was very concerned about the incidents.
"You have to worry for the residents of the building. They are living in fear now," he said.