Two men in their 30s and 50s, and a woman in her 20s were arrested.
Three people have been arrested in connection with an arson attack on a vacant pub in Dublin on New Year's Eve.
The Shipwright pub and guesthouse in Ringsend was being renovated to provide emergency accommodation for homeless families.
Gardaí carried out four searches of residential properties in Dublin this morning.
Two men in their 30s and 50s, and a woman in her 20s were arrested on suspicion of arson for offences under the Criminal Damage Act.
They are being detained under section four of the Criminal Justice Act and can be questioned for up to 24 hours.
There has been rumours at the time of the Shipright fire that the building was going to be used to accommodate asylum seekers.
However these were unfounded and the property was to be used to house homeless families.