The NFC West side re-signed the linebacker, having initially released him last month after he was handed a ban for breaching the league's performance-enhancing substances policy.
The 28-year-old told the team's website: "It's a pleasure to be back. I miss being with these guys and being in this locker room. That's one thing you miss when you're away, just the camaraderie and being able to play the game you love.
"I'm definitely thankful to have the opportunity to come back and I appreciate it. This is obviously the best situation for me in terms of playing and knowing the defense and the guys.
"I'm just going to play the way Jo-Lonn plays. Just play with some fire, hair on fire, get after guys. As I've said plenty of times, there's a winning team in this locker room, a playoff team in this locker room. That's something we've got to prove, but I'm just looking forward to getting back and helping in any way possible."
Dunbar made 115 tackles, 4.5 sacks, two forced fumbles and two interceptions last season.