The DPA news agency reported that the six-wheel Syrian truck came under attack late on Wednesday in the Hazamieh Christian district, 10km from Beirut.
Witnesses said the truck, with an Aleppo Syrian licence plate, was parked with no one inside.
There were no reports of injuries.
Lebanese police rushed to the area to investigate the incident while fire trucks with wailing sirens headed to put out the blaze.
Meanwhile, two hand grenades were thrown at a hangar where Syrian workers reside in a nearby area in the Hazamieh district.
There was no immediate word on casualties, as police sealed off the area.
Similar attacks on Syrian workers have been carried out since last month's assassination of former prime minister Rafiq al-Hariri.
The opposition has blamed al-Hariri's killing on the Lebanese and Syrian intelligence, but have urged against "hate crimes" against some 400,000 Syrian workers in the country.