Yes, an executor can be a beneficiary of a Will.
An executor of a Will is someone who is in charge of reviewing the Will and deciding which assets need to be distributed amongst those who will inherit from the Will.
On the other hand, a beneficiary of a Will is someone who benefits from the proceeds of the Will. They will inherit items within the Will such as money or property. It is normal for people to appoint a beneficiary as an executor of a Will too.
For example, it is usual to leave items in your Will to your children and have the eldest child as the executor.