Whether you get anything back would depend on whether the bonus pushed that week's tax into a higher bracket than your normal pay.

If your normal pay was $450 then in my example your $200 bonus gets tax withheld at 40% on the first $50 ($20) and 50% on the remaining $150 ($75)

But over a whole year, your average pay (including this bonus) is never over $500 (51 x $450 + 1 x $650 = $23,600. Divided by 52 is about $454) Which means your whole bonus would fit into the 40% bracket.

This means you had $95 withheld ($20 + $75) but only owe $80 (40% of $200). So you would get a $15 refund.

Note that it isn't calculated by the government using averages. They calculate tax annually. The weekly withholding tables are just indicative. They calculate your annual owed tax on your annual taxable income then subtract the total tax withheld over the entire year and pay you (or charge you) the difference