It happened around 10:00 a.m. Tuesday at the Max Studio at 1616 Walnut Street in Center City.
The female victim told police she was behind the counter with one customer in the store.
That's when a man, said to be in his 50's, walked in and made undisclosed comments to the clerk.
The victim then told police the man went behind the counter, groped her and lifted her skirt.
The man fled the store but was caught just moments later by police at 1606 Walnut Street.
The name of the man being held has not yet been released.