Yes, even if you haven’t completed your CBT, you will still need to have bike insurance.
You don’t need to have passed your CBT to ride a motorcycle, however, you will be restricted to mopeds up to 50cc.
Whatever type of bike you ride, you must ensure that it is insured when riding on the road. Failure to insure a bike before or after you complete your CBT will result in a range of penalties including fines, penalty points, and even bans.