During routine checking of vehicles in Exhibition Road, the cash was seized from a car registered in the name of the husband of BJP MLA from Paliganj, Usha Vidyarthi, Senior Superintendent of Police Vikash Vaibhav told PTI.
The occupant of the car could not show valid document in support of the cash, the SSP said.
The Income Tax department has been informed about the recovery of the cash in violation of the model code of conduct, the SSP said.
"The cash belonged to a petrol pump owned by my relatives which they were going to deposit in a bank", she said.
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She said relevant papers were being shown to the probe officials in support of their claims.
Vidyarthi is a two term MLA from Paliganj seat in Patna district.
The police and Income Tax department are keeping a close watch on movement of cash above Rs 50,000 without supporting documents across Bihar in view of the forthcoming Assembly elections.
Unaccounted cash is being seized almost daily.