What is the amount of the check you received? Sometimes, if you no longer work for a company, and the amount in your 401(k) is less than $1000, the investment company will automatically disburse the amount to you. In that case, it does have to be reported as taxable income.
But it usually does take them a few months to disburse the funds. One way to avoid this is to roll the funds over from the 401(k) into a rollover IRA after you leave a job.
