In California; no fed tax taken from paycheck. Do I pay this later?

The proper amount was withheld. The proper amount is zero.

His workers comp isn't taxable.

If you're talking about YOUR paycheck, you might be ok - you probably didn't make enough to owe any income tax. If they didn't take out social security and medicare though, ask them what's going on.

According to an online IRS publication (see link below) "Amounts you receive as workers' compensation for an occupational sickness or injury are fully exempt from tax if they are paid under a workers' compensation act or a statute in the nature of a workers' compensation act." Though you might want to make a call to your usual tax preparer to be certain...and to be appropriately prepared when tax season does arrive.

LDS: If required you will pay by 4-18-11

This advice was prepared based on our understanding of the tax law in effect at the time it was written as it applies to the facts that you provided. Click on my profile to read more. Errol Quinn Enrolled Agent

it is possible his gross was low enough with the dependents he claimed that no income taxes were withheld, there are minimums in each pay period and by status that no income taxes are withheld

and it isn't you who pays it, it is the two of you, you file a married joint return, each is a co taxpayer, neither is a dependent

WC benefits are not taxable income.