No not deductible.
But - If you work more than one job, you run the risk of having too much SS withheld. Each employer doesn't know what the others pays you. Tax time reconciles this.
And much thanks to Dilip for the following clarification - Not only does each employer not know what the others pays you, but even if you tell him, he will not care. He is required to withhold Social Security tax on the wages he pays you (and send in an equal amount as his contribution) regardless of what anyone else pays you. If the sum of your taxable wages from all employers exceed the maximum wages subject to Social Security, the excess withholding is credited towards the income tax due (and thus reduces the amount to be paid or increases the refund you are owed) but the employer's (excess) contribution that he sent in is not returned to him.....
Also, there is no such things as excess Medicare tax having been withheld
because there is no maximum wage beyond which Medicare tax does