Yes. There are a whole number of reasons a speedo could be reporting the wrong speed. The most common cause of errors is when the tyres (or wheels) have been changed to ones with different diameters to stock but tyre wear, temperature, vehicle load can all effect the accuracy. Also manufactures usually calibrate the speedo to over indicate speed by the average error of the speedo which can be +/- 10% so in the worst case scenario it could be out by 20%. Probably worth getting it checked out.