Is muscle mass supposed to be high?

The guideline variables on your scan are developed using world health organization standards against your height, age and gender.  These are only normative values of an average population.  Being high in skeletal muscle mass just means that you are higher in muscle than the average person or your height, age and gender.

Given the research around having and maintaining higher lean body mass is well documented for anti-aging and improved general health, having a high muscle mass will typically be beneficial.  If you are undertaking weight resistance activity, you will generally have higher skeletal muscle mass than the average population.