Syrian warplanes bombed gunmen inside Lebanese territory on Sunday on the border between the two countries, Lebanon's official National News Agency reported.
There were no immediate reports of casualties.
"Syrian warplanes targeted groups of gunmen in the Wadi al-Khayl area in Arsal firing four rockets," the news agency said.
Shortly afterwards, Syrian aircraft carried out two further raids in the same area, it added.
The Lebanese army confirmed air strikes in "border areas" but made no mention of their target.
The town of Arsal and the area around it are largely Sunni Muslim, and residents sympathise with the Sunni-led uprising against Syrian President Bashar al-Assad.
The border is long and porous, and has proved an easy crossing point for smugglers, refugees and fighters.
In April, Syrian forces backed by allied fighters from the Lebanese Shiite militant group Hezbollah retook control of most of the Qalamun region, just across the border from Arsal.
But Syrian activists say hundreds of opposition fighters have taken refuge in the caves and hills in the border area, using it as a rear base from which to launch attacks inside Syria.
Wounded fighters are also brought to the area, and food, medicines and weapons are smuggled through it, activists say.
Two weeks ago, Lebanese army forces carried out raids in the area targeting militants with ties to "terrorist groups," an army statement said.