Dispatched at 1756 hours for a possible unattended burn across from the callers residence. 12-5-1 arrived on scene and stated the fire was heading towards the woods. 12-4-1 arrived and its crew started to extinguish the fire with the brush truck and indian tanks. 12-1-1 and 12-2-2 arrived and assisted. Investigation determined possible a passer-byer threw out a cigarette. Used approximately 750 gallons water, burned approximately 4 acres burned. 16 members responded, back in service at 1840 hours.