Is this an oxymoron?

Minimum of up to three years of full-time applicable work experience in municipal solid waste services administration or closely related field.

Is the phrase minimum of up to three years an oxymoron?

The phrase "minimum of up to three years" is not an oxymoron because an oxymoron is a concise paradox: a phrase of (usually) two words that contradict each other. Strictly speaking, the two halves of the oxymoron should be contradictory when interpreted literally, and the contradiction should be the "point" of the phrase--i.e., the reader should be impressed that such a thing could exist when logically it should not.

As stated by @Edwin Ashworth in the comments above

The 'up to' constraint doesn't make any sense here. It's tantamount to saying 'a minimum of some amount of time (but we're not saying what) between 0 - 3 years'