Indonesia as a country with a large number of motorcycle users, has a high accident rate where human factors involved in most cases. The dangerous behavior committed by motorcyclists is alleged to be one of major reasons of the accidents and incidents. Among all possible dangerous behavior carried out by motorcyclists, mobile phone usage while riding could bring a horrible consequence to the road safety. The purpose of this study is to investigate the effect of time period, road density, and rush hour traffic on the use of mobile phones while riding. Field observation was conducted to assess motorcyclist’ behavior in using mobile phone while riding. This research observed two level of road type based on its density. The observation on each type of road was carried out in the morning, afternoon, and evening by considering the rush hour at each observation. The prevalence of mobile phone use among the motorcyclist and passengers ranges between 1%~3%. A more detailed results on different observation variables will be discussed in this paper.