Can ct scan damage brain , effect activity of brain?

No: The x ray radiation in a CT has no measurable or known effect on neural tissues. 1) dose is way too low and 2) nerves are relatively radioresistant since the cells don't reproduce very fast, if at all. There is a theoretical risk of cataracts and cancer years later, but this is incredibly small esp. for a single scan and controversial anyway.

Unlikely: The amount of radiation in a single CT scan of the head is minimal and will not affect the activity of the brain, nor damage it structurally. The cancer risk is estimated to range from 0.05% (child) to 0.01% (adult) for a single CT of the head. Repeated exposure to radiation can affect the brain, and does increase the cancer risk. reference: http://www.nejm.org/doi/full/10.1056/NEJMra072149