"Microwaves are electromagnetic waves with a frequency of about 2.45 GHz and a wavelength of about 12.2 cm; in the electromagnetic spectrum, they fall before infrared light but after radio waves (Heckert 2007). In a microwave oven, microwaves are produced by a device called a magnetron."
"The 2.4 GHz Part 15 band in the U.S. allows spread-spectrum operation as long as the 50 dB bandwidth of the signal is within the range of 2,400–2,483.5 MHz"
So yes, a microwave oven should and will interfere with 2.4 GHz WiFi devices.