WASHINGTON (AP) -- The federal government sent about 3,900 economic stimulus payments of $250 each this spring to people who were in no position to use the money to help stimulate the economy: prison inmates.

The checks were part of the massive economic recovery package approved by Congress and President Barack Obama in February. About 52 million Social Security recipients, railroad retirees and those receiving Supplemental Security Income were eligible for the one-time checks.

Prison inmates are generally ineligible for federal benefits. However, 2,200 of the inmates who received checks got to keep them because, under the law, they were eligible, said Mark Lassiter, a spokesman for the Social Security Administration. They were eligible because they weren't incarcerated in any one of the three months before the recovery package was enacted.

"The law specified that any beneficiary eligible for a Social Security benefit during one of those months was eligible for the recovery payment," Lassiter said.

The other 1,700 checks? That was a mistake.

Checks were sent to those inmates because government records didn't accurately show they were in prison, Lassiter said. He said most of those checks were returned by the prisons.

"We are currently reviewing each of those cases to determine whether or not the recovery payment was due," Social Security Commissioner Michael J. Astrue said in a statement issued Wednesday evening. "Where we determine payment was not due, we will take aggressive action to recover each of these erroneous payments."

The Boston Herald first reported that the checks were sent to inmates.

The inspector general for the Social Security Administration is performing an audit to make sure no checks went to ineligible recipients, spokesman George E. Penn said.

The audit, which had already been planned, will examine whether checks incorrectly went to inmates, dead people, fugitive felons or people living outside the U.S., Penn said.

The $787 billion economic recovery package included $2 million for the inspector general to oversee the provisions handled by the Social Security Administration. The audit is part of those efforts, Penn said. There is no timetable for its conclusion.

The federal government processed $13 billion in stimulus payments. About $425,000 was incorrectly sent to inmates.