It is not possible to determine the cause of a black spot in the mouth without a proper clinical examination. Such a spot can have several possible reasons — some are harmless, while others may need further evaluation. Since no picture has been shared and an in-person examination is essential.
Next Steps
I would strongly recommend you visit your dentist or an oral medicine specialist for a proper check-up.
Health Tips
If you notice any changes in size, color, or if other symptoms develop, please seek care promptly.