Unless one is a seasoned user of modern FLASH-based microcontrollers, the answer is not SO straighforward.

P89V51Rx2 does NOT have a built-in EEPROM. So, it seems that answer is NO.

However, it's FLASH is erased in 128-byte chunks (sectors), it's endurance is 10k cycles. Sector erase takes 30ms and byte programming 50us. There is plenty of user FLASH, but if for some reason the data should NOT be located there, some space can be found also in the bootloader FLASH (this is not supported by the builtin IAP but doable).

This is fully suitable for many applications where a few "setup parameters" have to be stored only from time to time (or only once).

Jan Waclawek