The operation cannot be performed on database "your_database_name" because it is involved in a database mirroring session or an availability group. Some operations are not allowed on a database that is participating in a database mirroring session or in an availability group. ALTER DATABASE statement failed. (Microsoft SQL Server, Error: 1468)
If you try to delete a database before removing it from an AlwaysOn Availability Group, then this error occurs.
To avoid from this problem, first you should remove the database from the Availability Group that contains it and then delete the database.