No, a TSP is not an IRA.

A Thrift Savings Plan is a retirement savings and investment plan for federal employees and members of the uniformed services. It is a defined contribution plan, which means that the retirement income you receive from your TSP account will depend on how much you put into your account during your working years and the earnings it accumulates over that time. The TSP is designed to give federal employees the same retirement savings related benefits that workers in the private sector enjoy with 401(k) plans, with contributions automatically deducted from each paycheck.

TSP