A non-competition agreement is a contract. Like any other contract, it is  governed by its terms or language--that is, by what it says. If it only states that it applies after your employment ends, then it would only apply after your employment ends; however:1) Make SURE that's what it says; and2) Bear in mind that your employer could choose to legally terminate (fire) you if it becomes aware that you are working for a competitor simultaneously--that's because unless you have a written employment contract which prevents termination in this circumstance, you are an "employee at will" and may be terminated at any time, for any reason whatsoever. So if your employer would disapprove of this, you could lose your job.