Most schools will ask you to satisfy background requirement by taking 3 or 4 core courses. You can pass this requirement either by (1) taking the course, and getting a B or higher grade; or (2) by appearing for the final exam and getting a grade of at least B.
For many schools, the core courses comprise of one course in systems (OS/Networking/Architecture), one in theory (theory of computation/algorithms) and one in applications (Artificial intelligence/Machine learning etc).
At some schools, the professors can waive these requirements if they feel you have enough background. Sometimes, they ask you to take an oral exam.
Since your UG degree is in Civil Engineering, it might be difficult for you to convince them that you have enough background in systems part unlike ECE students - most ECE undergraduates would have taken a course in Computer Architecture.
All the best!