Five periods characterize the temporal variation of the quality factor of seismic coda waves attenuation Q_C^(-1)(Q_0^(-1)) at 9 Hz and lapsed time of 30 seconds, before the Nyamulagira eruption of 6 November 2011 in the Virunga volcanic region of eastern Democratic Republic of Congo. The period I (January March 2011) was characterized by low attenuation. It grows during period II (April August 2011) to reach a maximum on the period III (September October 2011) and decreases during period IV (01 06 November 2011). A significant decrease in attenuation characterizes the period V (7 November 2011 January 2012). An average attenuation growth preceded the magmatic eruption for about 7 months, with a transitional period (III) of maximum attenuation less than 2 months (46 days) before. This period corresponds to the emplacement of the magma in a confined storage area or into a shallow magma chamber and the creation of new fractures/cracks. A drop of attenuation is observed two days before the eruption after a total saturation of the fluid in fractures/cracks (period IV). Periods (I III and IV V) correspond respectively to the magmatic intrusion and eruption. The variation of the frequency parameter of Coda wave n indicates a change in the degree and dimension of fracturing over time. The significant differences between periods illustrate the change in volcanic activity in the Virunga region.