Induction cooktops contain electromagnets below each pot or pan station. When a station is switched on, electric current flows through wire wrapped around an iron core. In order for magnetic flux to be induced in the iron core, the electric current must constantly change, so the current must alternate. The iron core concentrates the magnetic flux generated by the electric current, and a magnetic field is created on the cooktop.
If you place a ferromagnetic pot or pan above the electromagnet, the changing magnetic field induces electric current in the pot or pan. The induced current swirls around the pot or pan and dissipates its energy against the electrical resistance of the pot in the form of heat.
If there is no pot or pan on top of the electromagnet, no electric current will be induced, but the electromagnetic field will still exist, and the circuit will still draw current according to Ohm's law
$$I = V / R$$
where $I$ is current, $V$ is potential difference across the circuit, and $R$ is resistance.
Induction cooktops must have time changing current in order to generate a magnetic field, so the simple Ohm's law must be altered to include capacitance and inductance. The result is that resistance is replaced by impedance.
Nevertheless, the idea is the same, and even without inducing electric current above it, the electromagnet will draw current which is directly proportional to the voltage input, and indirectly proportional to the impedance. The amount of current drawn by the electromagnet when there is no pot being heated will be minimal, as Daniel pointed out in his answer.
Induction cooktops have automatic circuits which shut off the electromotive force to a cooking station if there is no pot or pan on it. But in the absence of such a shut-off, current would continue to be drawn, though an insignificant amount with no pot being heated.