Hey,

Yes, you are eligible for RBB technician post. There are two posts in RBB as a technician -: Technician Grade III Signal and Technician Grade III Telecommunication. 

•The only eligibility criteria to apply for this post is that you must have passed 12th with physics, chemistry, and Mathematics.

Well, as you are an engineering graduate, you can apply for other posts in Indian Railways also.

All the best!