They are typically scaled integers and have not been calibrated/atmospherically corrected to surface reflectance but the way to be certain is to ask your data provider what processing has been applied to your product. You can use the Radiometric Calibration tool to apply the metadata scale factors to the data to convert it to radiance or top-of-the-atmosphere reflectance. Then use a tool such as FLAASH or Quac to calibrate to surface reflectance.