Investigators have nicknamed those responsible as the "Big Top Bandits" because of their clothing, including a variety of hats.
FBI spokeswoman Ayn Dietrich says handguns were pointed at customers or employees during the robberies.
During a May 22 robbery in Seattle, one robber fired a shot inside a bank. During a June 8 robbery in the south Seattle suburb of Burien, a robber hit a bank teller in the face.
The FBI says 47-year-old Jeffery Lamont Pool of Wichita Falls, Texas, and 23-year-old Luther Ray Leonard of Renton, Wash., were arrested Monday in Renton. Dietrich says Pool is also wanted on several arrest warrants out of Texas related to armed robberies in that state.
The "Big Top Bandits" are blamed for five bank robberies this year.