Irish police said Saturday they had charged a man in his 40s arrested after an explosive device was found in a vehicle near the border with Northern Ireland earlier this week.
He was due in court in Dublin late Saturday, said Ireland's police force, known as the Gardai.
Police said on Friday they had charged the car's driver, a 25-year-old law student with possession of explosives.
Isobella Perrie Sullivan, of County Kildare west of Dublin, was stopped on the road and a bag was discovered in the back of her car containing the plastic explosive Semtex and a detonator, Trim District Court heard late Friday.
Her lawyer said she had been asked to take a bag north but had not been aware what was in it.
Officers flagged down the car as part of an operation targeting "dissident republican activity", police said. They have described the discovery as "extremely significant".
Northern Ireland was torn apart by civil conflict between the pro-Irish republicans and the pro-UK unionists until the Good Friday Agreement in 1998.
The agreement required rival paramilitaries to decommission their weapons, but dissident factions persist on both sides.
Dissident republican groups are smaller than the Provisional Irish Republican Army, which ended its violent campaign in 2005, but have used improvised explosive devices and mortars in past attacks.
Earlier this year, Northern Irish police blamed dissident republicans for two separate attacks on police stations near Belfast which caused no casualties.