If my father claimed my mother only to get back tax withheld from a pension can I still claim my mother because I supported her?

[MarilynG1]

If you provided over half of your mother's support, then you can claim her as your Dependent. 

If you father already claimed her, though, you won't be able to Efile your return and will need to mail it in.

The IRS will contact both you and your father to determine who had the legitimate dependent claim for your mother, and the one who doesn't will have to pay back any refund related to this claim.