It's a common phrase used to express doubt or to confirm something.
Here are some examples:
* "¿Estas seguro de que quieres ir?" (Are you sure you want to go?)
* "Estas seguro de que esta es la dirección correcta?" (Are you sure this is the correct address?)
It's important to note that the pronunciation is slightly different from the English "Are you sure?". The "s" at the beginning of "estas" is pronounced with a soft "s" sound, similar to the "s" in "sin" in English.