On November 11, 2018, an event generating long-lasting, monotonic long-period surface waves was observed by seismographs around the world. This event occurred at around 09:30 (UTC) east of the Mayotte Island, east Africa. This event is unusual due to the absence of body waves in the seismograms and people’s lack of sense. The purpose of this study is to investigate this unusual event using the waveforms recorded by the Iranian National Broadband Seismic Network. The network consisted of 26 stations in operation on November 11, 2018. The stations are located from 4542 km to 5772 km north-northeast of the event’s epicentre. The arrival of monochromatic long-period signals is visible around 10 UTC in the recordings of all the stations and lasts for more than 30 minutes. Frequency analysis of the seismograms shows a clear peak at 0.064 Hz (15.6 sec/cycle). The maximum amplitude of the transverse components is less than a half of the radial components. This is in agreement with the theoretical radiation pattern of Rayleigh and Love waves at a frequency of 0.06 Hz from a vertical Compensated Linear Vector Dipole (CLVD) source mechanism. The average apparent phase velocities are calculated as 3.31 km/s and 2.97 km/s, in the transverse and radial directions, corresponding respectively to the Love and Rayleigh waves in the range of 0.05 to 0.07 Hz. The surface wave magnitude of Ms 5.07 ± 0.22 was estimated. Just before the monochromatic signal, there is some dispersion in the surface waves. This observation may suggest a regular earthquake that triggered the strange Mayotte event.