Is it possible to get admission to masters for theoretical physics with a bachelors in electronics engineering? Can I get into masters for theoretical physics without having a bachelors in physics or maths? I have a bachelors in electronics engineering, and I can get a recommendation from the physics department for the admission.
Absolutely. On a Masters course you will meet people from a wide range of backgrounds. In fact, one of my physics students has just been accepted onto a Masters course in computer science.

Having said that, you may struggle to get onto a good course if your grades are not strong. Since you will have a lot of catching up to do, those running the Masters programme will need to be persuaded that you're hard working with good potential. You will also probably need to demonstrate that you've already made an effort to study theoretical physics (e.g. discussing in some detail the topics that interest you in your application).