No matter what kind of exercise you are doing or how light fabric clothes you are wearing, it is common to sweat while pumping iron or running on the treadmill (or even while brisk walking or outside cycling).
Sweating is a natural phenomenon and is inevitable.
The problem is that most people consider sweating as a parameter to measure how hard they are working in the gym and how effective their workout routine is.
They believe that the more you sweat, the more calories you burn.