The Hairspray star was charged with both misdemeanours in Los Angeles earlier this month (Sep12) after allegedly colliding with a police car in April (12) and a second vehicle in August (12), leaving the scene of the crime each time.
On Thursday (27Sep12), her attorney entered the pleas on behalf of her client in California.
Bynes is due back in court on 19 October (12) and faces up to a year behind bars if convicted, according to TMZ.com.
The 26 year old still faces two counts of driving with a suspended licence and one count of driving under the influence. She is due to stand trial on those three charges on 29 October (12).