The UN agency's delivery - 1,000 tonnes of wheat - is being stored in a warehouse ready for distribution to the worst-affected areas north and west of the city.
Some of the trucks were stopped near the town of Sarobi on Thursday by robbers who stole money and personal possessions from the drivers.
A WFP official in Kabul said the security situation on the roads was still hampering the organisation's efforts.
Meanwhile, in northern Afghanistan, a convoy from the International Committee for the Red Cross (ICRC) completed the four-day journey from neighbouring Turkmenistan to the city of Mazar-e-Sharif.
The 59 trucks took 1,500 tonnes of aid for distribution to 65,000 people in and around the city.
This includes six weeks' rations of food for 5,000 of the most vulnerable families, as well as blankets, cooking sets and water containers.
The trucks also took six medical kits to help equip hospitals treating war-wounded in the region.
In addition, ten trucks have left Iran for the western city of Herat carrying non-food aid, the organisation said.
First airlift
On Friday the WFP carried out its first airlift of food aid to Afghanistan since 11 September.
The agency said it would fly four times a day from neighbouring Tajikistan, carrying food aid to the mountainous north-east of Afghanistan to feed some 300,000 people living in isolated villages already affected by winter conditions.
The deputy UN coordinator for Afghanistan, Antonio Donini, said the UN was trying to expand the presence of its international staff, but was first checking security had been restored in the various cities it operates in.
Mr Donini said security assessments had been conducted in Kabul, Faizabad and Mazar-e-Sharif, and that he hoped one would be under way in Herat in the next couple of days.
Race against time
Mr Donini said the overall situation in Mazar-e-Sharif was still fragile, but there was a sense that it was improving.
If conditions there remained "benign" over the next few days, international staff could be back in Mazar more permanently within a week, he said.
The UN had received assurances concerning the safety of its operations in the area, although agency offices were looted both before and after Mazar was taken by opposition forces.
Mr Donini described the humanitarian situation in northern Afghanistan as a crisis of stunning proportions.
He said it was a race against time and that all corridors for delivering aid would be used as they became available.