AddRigidBody Script Error

I have an AddRigidBody script for an FPS zombie game, and it has this error.
I’m not even really sure what this means, nor can I find it anywhere on the internet.
The error: " Assets/Scripts/AddRigidBody.cs(8,17): error CS0029: Cannot implicitly convert type UnityEngine.Rigidbody' to AddRigidbody’ "
And my script:

using UnityEngine;
using System.Collections;

public class AddRigidbody: MonoBehaviour {
	public float mass;
	public AddRigidbody rb;
	void Start() {
		rb = GetComponent<Rigidbody>();
		rb.mass = mass;
	}
}

Just to clear it up, both of the objects have non-trigger collisions. The object is a zombie and the second object is a wall. They just kind of go right through the walls, instead of stopping like the Player.
Thanks

On line 6, you are trying to set your gameObject’s Rigid body as an AddRigidBody, so you shold change that line to public Rigidbody rb;. I’m not sure if you’re familiar with objects, but when you create a class, you can create a new object (which isn’t Unity specific, like GameObject), which is why you would use new GameObject () or in your case, new AddRigidBody (), so I hope this clears some things up for you.