Hey,
First off, you need to be sure of your calling. Just ask yourself what interests you the most and it's scope in the present times and work accordingly.
See, since you are already pursuing Bachelors in computer science, so it would be any better if you choose the same stream in your masters as IT industries have lots of scopes nowadays.
Havint said that, you can also go for Masters in Physics, if you genuinely like the subject and want to  learn more about it but if you are looking for an immediate success in terms of job, then you would have to wait.
Hope this helps.
Good luck.

Hello.
As you chose computer science as a specialised subject for your B.Sc then it would be wise decision to go with same for master and if your interest deviate you then try to see in yourself where your interest goes, if you like coding and jobs in CS area then don't think go for MSc in CS while if you like to research on physics topics , finding why and how of University happenings then go for MSc physics but as it is masters then you will have good job options
Best of luck.