This means that subscribers have up to September to register or correct any anomaly with their registration.
The exercise was originally scheduled to end on June 30, this month to pave way for Mobile Number Portability.
Speaking at a press conference on Monday after a meeting with Chief Executive Officers of the telecom operators, Mr Paarock Van Percy, Director-General of the NCA said the 90-day window was to give opportunity to people with invalid data to correct the anomaly.
Nearly 18 million mobile subscribers have registered out of which between six and seven million are deemed invalid because of faulty data.
Mr Van Percy said the NCA would use the period to complete the exercise and clean up the register of invalid data.
He said the registration exercise was not intended to be punitive or for individuals to lose their SIM cards.
Mr Van Percy said individuals with registration anomalies would not be able to receive confirmation to port their numbers when the Mobile Number Portability is launched on July 7.