I feel vibration, especially in the steering wheel, in high speed.
Could this be a wheel alignment problem?

 

alignment - not directly. vibrations are created by the rotating parts - ie wheels, axles, motors (via a broken mount). Not maintaining the alignment can cause tire wear which can lead to vibrations as can bad shocks or worn suspension components. A few tests and tips. Does the vibration change when lifting the gas or going full power at speed? Does the vibrations change in a left hand sweeping turn vs a right hand turn? Does the vibration change when you apply the brakes? Another tip is to do a front to rear tire rotation (left front to left rear etc) and see if the vibration changes. Do a quick visual inspection under the car: any signs of oil leaking from the axle boots? Is the exhaust system secure? With a helper, open the hood, have one person in the drivers seat and the other watching the engine (standing to the side of the car). start the car and "power brake" the engine (brake on full so the car doesn't move and give it some gas) Any excess motion or lifting of the engine?

This should help you give some into to your shop regarding when you feel the vibration to help them with their diagnosis.

 

I'm responding as the OP for posterity's sake.

I took my XC60 to the dealership, and they said the front wheels have been deformed probably due to going over pot holes, of which there is no shortage here in the Northeast.
They switched the front wheels with the rear wheels, and the vibration has definitely decreased.
But it's only a makeshift measure, as now the back seat passengers will feel the vibration more instead.
We're going to wait out until we need to replace the tires anyways.

 

you may be able to have the wheels balanced but if they are bent you may need to find a wheel shop to straighten or replace the wheel in question.

here's one example of a shop that does repairs - https://www.wheelcollision.com/