Robotic rehabilitation systems that provide proprioceptive information offer a promising approach to helping stroke survivors regain lost proprioceptive functions. One potential way to provide proprioceptive information is viscosity rendering. However, how the modulated viscosity rendering affects brain activity remains unclear. To investigate the correlation between viscosity rendering and brain activity and to provide a neurological basis for the design of robotic rehabilitation systems, an experimental setup was developed to deliver various viscosity rendering and fixed stiffness rendering during hand movement. In the experiment, twelve healthy participants interacted with virtual bottles with the same bottle stiffness but filled with liquids of different viscosities under the same movement speed, providing different levels of proprioceptive information in the form of force on muscles and joints. Control conditions without viscosity and stiffness rendering were also tested, involving both passive and active hand movements at the same speed. Results showed that stronger mu-ERD and beta-ERD were observed during movements with viscosity and stiffness rendering compared to control conditions. No significant evidence suggested that different viscosity in rendering caused variations in mu-ERD or beta-ERD. Additionally, no significant differences were found between active movement without haptic rendering and passive movement in EEG activities. These findings suggest that while the existence of viscosity and stiffness rendering during movement strengthens brain activity, modulating viscosity rendering does not significantly affect this response. This insight is particularly valuable for designing robotic rehabilitation systems that incorporate viscosity rendering.