If you filed a joint return and you're not responsible for your spouse's debt, you're entitled to request your portion of the refund back from the IRS. You may file a claim for this amount by filing Form 8379, Injured Spouse Allocation.
You may file Form 8379 by itself after you receive notification of an offset. The processing will take about 8 weeks.
Be sure to attach the required Forms W-2 and 1099 for both spouses showing federal income tax withholding to avoid delays. Don't attach the previously filed joint tax return.