The mob, carrying flags and banners of "Bundelkhand Adhikar Sena", first raised slogans against the Congress outside the party office in Mall Avenue area and then barged into the premises.
They attacked Congress workers and vandalised the office. Furniture and flower pots were broken, and cars and two-wheelers were damaged.
Among those who were roughed up was party leader Dwijendra Tripathi.
Party spokesman Rajiv Tyagi said the party workers were unable to figure out why the attack took place.
He said that Bundelkhand received a multi-crore-rupee package at the behest of party vice president Rahul Gandhi, and the attack appeared to have been plotted by political adversaries.
A probe has been ordered into the incident and a report sent to the Election Commission, an official said.