Hi,
Thank you for posting your query.
It is not uncommon for 
CT scan of brain to be normal in cases of 
epilepsy. However, the detailed evaluation of your son should include MRI Brain-epilepsy protocol and electroencephalogram (EEG). 
At present, he is on low dose 
keppra and the dose may be increased in consultation with his doctor for better 
seizure control.
Please get back if you require any additional information.
Best wishes,
Dr Sudhir Kumar MD (Internal Medicine), DM (Neurology)
Senior Consultant Neurologist
Apollo Hospitals, Hyderabad,
My personal URL on this website:  http://bit.ly/Dr-Sudhir-kumar 
My email: drsudhirkumar@yahoo.com