It depends- if your income is too high to deduct the IRA contribution, then yes, it is. Or, you may opt to make it non-deductible. Usually this is done if you wish to convert it to a Roth IRA. Finally, if you wish to deduct this IRA contribution, then no, it is not a nondeductible contribution.
Here is some more information about IRAs: Deductions Allowed for Contributions to a Traditional IRA