The blast, which targeted an open area near the entrance of Zahle, a predominantly Christian town, did not appear to have a military or political target.
There have been attacks of this kind in the area, usually targeting Lebanese army or Hizballah convoys.
The Lebanese Red Cross, which often operates as the main paramedic service in the country, confirmed one woman was killed and ten others were injured.
Security forces have cordoned off the area and launched an investigation.
The bombing comes about two weeks since a roadside bomb blamed on Islamic State wounded five soldiers traveling in a military vehicle in Lebanon's northeast border region.
In June, eight suicide bombers blew themselves up in the border village of Qaa, just north of Arsal, killing five and wounding dozens others.
Hundreds of militants, some affiliated to IS and other jihadist groups, are thought to be holed up in the rugged hills that straddle the Lebanese-Syrian border.