Yes of course you can go through robotics in M.tech after completing your B.tech in Civil engg .But there are very few Institutes which offers you the robotics course in India.
Some of them namely are:-

IIT ( Delhi,Kanpur,Chennai,Mumbai,Kharagpur,Guwahati,Roo rkee )
Jadavpur University
SRM university
PSG college of technology
Birla Institute of Technology and Science

Prepare well for GATE so that you can get selected in IIT's,NIT's or other such good Institutes.Some of the deemed Universities offers a seat through a separate entrance test conducted by them.

M. Tech. in Robotics Engineering: Course Highlights

Dear aspirant,

That can be donw very easily. When you fill the form for Gate make sure you fill it for robotics stream if that's available. Clear the exam, for robotics you'll have to have the knowledge of coding andother basic logic designs that are needed or are taught to those who persue Btech in robotics 2nd to 4th year. Once you've gained the knowledge, You can clear the gate for robotics stream and join MTECH programs in robotics.

All the best