Viscous force is somewhat like friction as it opposes, the motion and is non-conservative but not exactly so, because

Viscous force is somewhat like a frictional force but not exactly the same because it differs from it due to the two main following statements: 

i. Viscous force is proportional to velocity gradient while frictional force is not. $\left(viscous force,F_v=-\eta A\frac{dv}{dx}\& f=\mu N\right)$

ii. Viscous force is temperature dependent as with rise in temperature, coefficient of viscosity for liquid decreases while that of gases increases. But  frictional force is not dependent on temperature.