Look at the number of keys on the keyboard. Digital keyboards can have as few as 25 keys or as many as 88. Digital pianos have the full 88 keys of a standard piano keyboard, and most workstations have at least 61 keys or more.
I would not recommend learning to play piano on a keyboard. ... Keyboards today allow you to transpose all of the keys up or down an octave, which may help for some pieces, but generally, for classical music, 61 keys isn't enough. However, you might not need 88 either. There are also 76 key keyboards.
There is no standard computer keyboard, although many manufacturers imitate the keyboard of PCs. There are actually three different PC keyboards: the original PC keyboard with 84 keys, the AT keyboard also with 84 keys and the enhanced keyboard with 101 keys.