I have two product brand. For example:-

Product A - Nestle Brand (Table A)
Product B - Cadbury Brand (Table B)

I have an order table with the attributes:

-id
-orderNo
-foreign key reference to table A
-foreign key reference to table B
-quantity
-createdDate

The data base on the attribute above:

1,1001,1,null,20,20/12/2011
1,1001,null,1,20,20/12/2011

Does my design make sence?

Thank You.

What is the reason for having two product tables ?

@OP: No, your design doesn't make any sense at all.
pritaeas has a valid point, but there is also the issue of having the same info on 2 different fields which will make your life difficult in the following steps.

Although you didn't explain what this is about, I can't help but notice what will you do if you find yourself with 5 brands or 50 brands.
In my book there is only 1 product table and when dealing with a product (brand or whatever) you go to that table. If additional info is required, you can create tables with specific functions (MSDS, packaging data, UPCs, photos, kitting/manufacturing info, etc) around that product master (or item master).

What is the reason for having two product tables ?

The reason is because two product tables have a different structure of information.