Yes, there is a considerable risk of terrorism in Ethiopia. Extremist groups such as Al-Qaeda and Al-Shabaab have a growing presence across East Africa. Border areas with Kenya and Somalia present a higher risk to western travelers and should be avoided where possible.
There is a reasonable risk of terrorism in Addis Ababa. It is likely extremist organizations have the capability to mount attacks against westerner travelers if the opportunity is presented. Although the last terrorist attack in Addis Ababa occurred in 2013, it is important to remain cautious of the threat and consider the risks when located in heavily westerner hotspots.