David Byrne was shot at the Regency Hotel in Dublin on 5 February.
The men, both aged in their 50s, are being questioned at Ballymun and Clontarf police stations.
In total, seven people have been arrested as part of the investigation into Mr Byrne's murder.
Irish police believe at least six people were involved in the attack at the Regency Hotel, which left two others wounded.
One man, 24-year-old Patrick Hutch, has been charged with Mr Byrne's murder.
Two men have been arrested by police investigating the murder of a man at a boxing weigh-in event in Dublin.