Honda Civic Steering Wheel Shakes at High Speed

Hi! My wife drives a 2010 Honda Civic LX sedan with about 18k miles. She mentioned that its steering wheel started shaking a couple of weeks ago when driving at about 60 miles/hour at the same streth of the road during her daily commute. She did experience the problem during rest of her drive at lower speed. I drive the car about once a week at lower than 45 miles/hour and had no problem. I have checked the tires and noticed nothing obvious. I wonder what the problem could be. Thanks very much for your time and help in advance.

Probably lost a wheel balancing weight. Have the tires balanced and rotated ASAP.

Might be free under warranty. Otherwise should cost no more than $50. Maybe less.