A few things for you to check first:
Please check your tyre pressures are the same all round in the 32-36 psi zone.
32 for comfort, 36 for fuel economy.
Can you look at the tyre tread depth, are they even front tyres to back tyres? About the same wear?
If all this appears to be normal, I'd say by your description the car has an electronic issue, ABS wheel speed sensor, SAS, (Steering Angle Sensor), or Multi-Axis sensor etc.
So I would suggest if you see no abnormality from your own observation as above, I would recommend a scan of vehicle to see if any codes all present in the ABS module, and go from there.
Toyota would do this for you for a small outlay.
Hope this helps.