The CBI in the mentalist stands for California Bureau of Investigation, initially I thought this was a regional office of the FBI, but it doesn't seem to be (no FBI-labelled jackets/body-armour etc...), it also seems only to be state-wide (California) and fairly small.
Is it a made-up/based-on police agency with state-wide powers or is there a CBI?
Apologies for any incorrect assumptions, I'm from the UK, not the US.