The "Defend Europe" vigilante scheme was announced by anti-immigration campaigners from France, Italy and Germany after they managed to crowd-fund the 76,000 euros ($87,000) needed to rent a boat.
The plan aims "to expose the true face of so-called humanitarian organizations, their collaboration with smuggling mafias, and the deadly consequences of their actions at sea," according to organizer Clement Galant.
- 'Are we really the problem?' Migrant aid groups challenge government response to crisis
- UN warns that Italy cannot handle migrant crisis alone
- Debunking myths about why people migrate across the Mediterranean
"When boats full of illegal migrants cross, our mission is to call the Libyan coastguard so that they can come and rescue them," he said in a video posted on social media.
"We will keep them safe in the meantime."
The United Nations' migration body says that 100,000 people have arrived in Europe by sea this year, the vast majority Africans departing from Libya.
Despite their humanitarian mission, aid groups have come under fire with some critics saying their presence encourages migrants to attempt the crossing.
The far-right group, which calls itself "Generation Identity", says the 40-metre (130-foot) vessel is en route to the Mediterranean after leaving Djibouti last week.
It will transport activists from the Sicilian port of Catania and patrol international waters off the coast of Libya.
The group managed to raise tens of thousands of euros by crowd-funding the initiative and rented the boat despite an online campaign by opposing activists who had demanded that PayPal freeze GI's account.
"By saving these peoples and providing an obstacle for trafficking groups, we can save Europe and save lives at the same time," said a GI spokesman.