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A comprehensive analysis of Visible Infrared Imaging Radiometer Suite (VIIRS) radiometric bias relative to Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) collection 6 data has been performed since early 2012 for selected reflective solar bands. The study suggests that VIIRS bias trends changes over time mainly due to calibration updates and anomalies. Results show nearly consistent biases of 1.7% for M5 (0.672 mu m) and 2% for M7 (0.865 mu m) throughout the mission. However, M1 (0.412 mu m) and M4 (0.555 mu m) biases are less consistent. While biases for both M1 and M4 fluctuates mostly around 0%, M1 shows most frequent short-term changes in bias trends, as high as 4%. When the bias trends are compared with VIIRS on-board-calibration-based gain trends, there exists a high correlation. In addition, the operational VIIRS data product of NOAA and the reprocessed NASA Land Product Evaluation and Test Element (PEATE) data were compared by trending the radiance ratio. The ratio trends show calibration differences that agree well with bias trends. The comparison of bias with F-factors and ratio trends indicates that the frequent changes observed in VIIRS bias trends are primarily caused by calibration updates and anomalies in VIIRS operational calibration. The study suggests that even though the operational VIIRS data archive meets the specification of +/-2% radiometric uncertainty, reprocessing can improve data quality needed for rigorous scientific applications.