Yes you can, but you rarely should.
If you do, save enough extra to pay for legal fees because co-executors are an excellent way to cause a lawsuit.
I often get this question from women with adult children. Some of the reasons I hear are: the siblings get along well, they won't disagree, the client doesn't want to have to choose between two.
Before we get too deeply into how to choose an executor, I like to ask: have you talked to your children? One may not have any interest in acting as executor and will not feel slighted in the least. Serving as an executor is a job with significant responsibility. It takes time out of the workday, it takes effort, and it takes financial management. Appointing co-agents can create confusion with banks, financial organizations, and title companies who want a single point of contact. Some documents will require both signatures or both agents to appear in person, which adds to the time and expense of probating an estate.
When choosing your executor, do your family a favor and don't appoint co-agents without careful consideration.