High-mass young stellar objects (HMYSO) displaying methanol maser flux variability probably trace a variety of phenomena such as accretion events, magnetospheric activity, stellar flares and stellar wind interactions in binary systems. A long-term monitoring of the 6.7 GHz methanol line in a large sample of HMYSOs has been undertaken to characterize the variability patterns and examine their origins. The majority of the masers show significant variability on time-scales between a week and a few years. High amplitude short flares of individual features occurred in several HMYSOs. The maser features with low luminosity tend to be more variable than those with high luminosity. The variability of the maser features increases when the bolometric luminosity the powering star decreases. Statistical analysis of basic properties of exciting objects and the variability measures supports an idea that burst activity of methanol masers is driven mainly by changes in the infrared pumping rate.