No, it's not required to register separately, to get MBBS seat in All India Quota. You just need to register on MCC (Medical Counselling Committee) https://mcc.nic.in. This registration will give you access to MBBS seats across most states under AIQ. 15% seats in all government medical colleges (except AIIMS, JIPMER, AMU, BHU, etc. which also participate via MCC) are reserved for AIQ.

But if you want to avail the State quota you may require to register for different state's counselling authority like

• Maharashtra (CET Cell)

• Karnataka (KEA)

• Tamil Nadu (TN Medical Selection)

• Uttar Pradesh (DGME UP)

• Rajasthan (RUHS)

Hope it helps