At least four suicide blasts hit the predominantly Christian village of Al-Qaa, a military source told AFP.
"The first attacker knocked on one of the homes in the village, but after the resident became suspicious, he blew himself up," the source said.
"People began gathering at the site of the explosion and the three other suicide attackers blew themselves up," he added.
A security source had said earlier that a bomb had exploded and then "more than one suicide bomber blew themselves (up)".
More From This Section
He said 15 other people were wounded, including some in critical condition.
Lebanon's national news agency said the blasts struck at 10 minute intervals and also wounded three Lebanese soldiers stationed in the area.
Al-Qaa is one of several border posts separating Lebanon and war-torn Syria.
The border area has been rocked by clashes and shelling since Syria's conflict erupted in 2011.
Lebanon's army has fought off jihadist factions along the frontier and has sought to clamp down on local cells operating in the area.
As they withdrew, IS and Al-Nusra kidnapped 30 Lebanese soldiers and policemen, 16 of whom were released after nearly 18 months of negotiations.