Dropping a course as a master's student I am planning to drop a course in my master's program as it has been really difficult for me to score well in it while looking for internships this semester.
If I don't drop it I will end up with a C in that course. I already have a B- and I don't want my GPA to drop.
How badly will it my hurt my future prospects when I am looking for jobs and internships?

I am a CS major and the course is related to my field.
The only repercussion you need to worry about is how much dropping the class will affect your standing in your program. If your program/school/advisor are okay with you dropping the class I see no further harm that will come from it. 

This being said, you will of course miss out on what is being taught in the class, which may indirectly affect your ability to get a job since you do not have some sort of required skill. 

But again, I have never had an employer ask me why I withdrew from a class.