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.
When contacted, the MLA said she had no role in the incident.
"The cash belonged to a petrol pump owned by my relatives which they were going to deposit in a bank", she said.
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.
Total unaccounted cash seized during the day stood at over Rs 16 lakh on Thursday.
6397 litres of illegal liquor was also seized.
Briefing reporters about the outcome of the drive, Additional Chief Electoral Officer R Lakshamanan said Rs 2 lakh was seized each from Bhojpur and Dumroan in Buxar in addition to Rs 12.36 lakh from a BJP MLA's husband's car in Patna.
The ACEO said the illegal liquor was seized during raids across the state.
One detonator was seized in Jamui, 1.5 kg contraband ganja was recovered in Madhepura besides 273 mobile phones in Gaya, he said.
Lakshamanan said 123 cases have been registered under Defacement in Public Property (wall writing, posters, banners), 10 for misuse of vehicle and 4 for violation of Loudspeaker Act.
Fourteen arms/weapons and 41 cartridges were seized, he said.
A total of 684 non-bailable warrants were executed, Lakshamanan said.