Yes, definitely! If you took both Computer Science and Yoga as an optional subject in your class XIIth board examination, then it is totally up to you regarding which subjects to include and which to exclude while calculation you best 5 subject percentage.

So, if you have comparatively higher marks in Yoga as compared to Computer Science, then you can surely use the Yoga as your fifth subject and use it in your percentage calculation.

Hope I have answered your question. All the best!