Maybe. We really need more information.
If you are referring to a 401(k) then generally yes if you are no longer employed by that company. There are various restrictions that may apply depending on the Plan Document. If you are referring to an IRA then again yes. An annuity might allow you to cash out if it has not been annuitized. A defined benefit plan may or may not allow you to cash it out and again depends on the Plan Document
In all cases, be very careful about taxes, penalties, and surrender fees as these costs can be significant.
Most likely, as John mentioned, if it is a 401k or an IRA you CAN cash in (401k you generally have to be no longer employed there) but that doesn't mean you SHOULD. Before you do, figure out how much you will need to pay in taxes and penalties. Do not rely on the amount the plan custodian may withhold. A 401k provider may required to withhold 20% for taxes, but this can be woefully insufficient if you are taking an early withdrawal (if you are not at least 59.5). If you do not plan for the tax bill, you may find you are in big trouble with the IRS next April 15th, owing lots of money that you may have already spent! Why can the tax be so high on early withdrawal? Well, first of all, the withdrawal is income and that additional income is added to any income you earned from employment during the course of the year. Adding the income together might put you in a much higher tax bracket. In addition, if you are not yet 59.5, you will owe a penalty of 10%, and if your state charges income tax, you will owe that too.
So two reasons NOT to cash in: It may cost a lot in taxes and you may be sacrificing your future financial security. Even if the amount is relatively small, it is usually good advice to leave it in place or roll it over into your new employers plan,, keep contributing to it, and let it grow and work for you.
Debbie, your question does not supply enough information to allow anyone on this board to give you an answer that applies to you. What it tells me is that you need to sit down with either financial planner who specializes in retirement planning or someone in your company's personnel department who knows the rules. There are an incredible variety of "retirement" plans and each one is different. You need to talk with someone who knows your plan.