Worcester boss Andy Preece made his move after losing his no.1 Danny McDonnell with an arm injury ahead of their game at Hucknall Town on Tuesday.
McKeown, 18, signed a two-year deal with Peterborough in the summer and is a regular in the Republic of Ireland Under-19 squad. He has already had a loan spell at Kettering Town this season where he played 2 games in the Conference North.
McKeown conceeded 5 goals in his Worcester debut in the defeat at Hucknall Town, where he played alongside on-loan Walsall youngster Peter Doran.