my pup keeps jumping on my border collies back i dont no if she is trying to mount her or if this could be a sign she maybe trying to domineer her.any ideas.

Without seeing her, my guess would be she's just playing!

it does look like that my collie doesnt seem to mind just carries on walking around but i dont think she will appreciate it when she is fully grown she is a bullmastiff lol.

I think most people are too quick to "Dominant"! She's just a pup playing and having fun. I wouldn't worry about it. Especially if your collie isn't. She knows what this means better than you do, so if she's not bothered you can bet it means nothing.

When your Collie gets fed up with it, I suspect it will make it's feelings known in no uncertain terms - Collies are not known for suffering fools gladly....

:D So true!