Yu Bi
Ansys Employee

The forces due to the additional damping will not be transferred to static structural, however, the structure acceleration which will be transferred to static structural to calculate the dynamic forces is calculated with the effect of the additional damping. This is the reason for the warning message.

Material properties and geometry decide the mass of the bodies in Static Structural. 

Not quite understand what is happening in the picture, however, if there is no option in the UI to turn it off, then it means it cannot be turned off. Please check the User's Manual for more information.