The six, who included two women, were riding in a Toyota Landcruiser when officers from Lagdera police station stopped them for a regular check.
Four others managed to escape after jumping off the moving vehicle in the 1 pm drama, police said.
The group was reportedly headed to Hagadera Refugee Camp when the recovery was made. North Eastern police boss Philip Tuimur said the suspects were escorted to the Dadaab Refugee Camp for further interrogation.
Other officers said there were reports the weapons and grenades were to be used in Garissa town for an attack.
Garissa has been the target of attacks by suspected terrorists who ambush and kill security agents, with up to ten dying in similar incidents in the past months.
The attackers usually use pistols to stage the assaults, with the latest taking place on Monday night where a soldier and civilian were killed. A third victim is fighting for his life in hospital.
The recovery was made a day after a man was arrested with six G3 rifles and 16 bullets in Elwak, Mandera at the Kenya-Somalia border.
The 53-year-old Somali national was ferrying the weapons on a donkey cart when police stopped him on Sunday afternoon. Also seized were six empty magazines and a spare barrel.
Police said the alien was transporting the weapons to Mandera, and later they were to be transported to an unknown destination.
The recoveries are the latest in the area as police work to stop terrorists from ferrying weapons from Somalia. A suspect was arrested in connection with the three soldiers’ killing in November and is facing various charges.
A parliamentary team is currently investigating the incident. The attacks are linked to a decision by Kenyan troops to cross to Somalia to hunt for Al-Shabaab militants, who had been blamed for various insecurity incidents in the country.
The troops now operating under Amisom have displaced the terror group from various places and are pacifying the occupied regions.
The government says most of the attacks are being staged by refugees who have sneaked out of their camps. In Nairobi more than 600 refugees were at the weekend arrested in an operation.
Nairobi Provincial Commissioner Njoroge Waweru said the operations are still ongoing until the aliens are apprehended.
Waweru said it was unfortunate that most of the people arrested had escaped from the Dadaab camp, which hosts refugees from Somalia.
Prime Minister Raila Odinga and internal security Permanent Secretary Mutea Iringo said the government was in consultations with UNHCR to have Somali refugees return to their country.