More than likely you have a tire out of balance. It is possible you have a bent wheel. Have your tires balanced, inspected, and rotated.
Wheel balance
check tires could have a busted steel belt in the tire or nothing more than a tire out of balance.
i would really like to know myself
the tires could be out of balence bent rim bad tire
If it happens when you are driving fast (60-70 MPH) it could be that your wheels are out of alignment.
a shake in the steering wheel could be a few things,a bad rim,broking belt in one of front tires,aliment,ball joints,or could be all of these thing Could be as simple as wheel balance but have the front end checked by a mechanic to be safe.
have your front tires rebalanced.
One or more tire out of balance, a bent wheel, or defect in a tire.
Tire out of balance, tire defect, bent wheel, defective wheel bearing, loose lug nuts, or worn suspension or steering parts.
Tire out of balance, bent wheel, loose or worn suspension parts. More than likely balancing & rotating your tires will correct this.
Wheel balance, Worn steering parts, Worn suspension parts, Tire damage,
Three things to check, Wheel balance, Alignment, or most likely the front rotors may be slightly warped.