The Robins currently lie in eighth place in the npower League One table, three points from the play-offs, and seven points behind joint leaders Tranmere and Doncaster.
Paolo Di Canio's men are without a win in their last three games, but Miller is confident the side can continue to keep pace with the division's best outfits.
He told the Swindon Advertiser: "We've had a few good results and a few not so good but we're still in the mix.
"There are still a lot of games but we've still got a chance. We're in there, we haven't dropped too far and a couple of wins and you're suddenly back in there."
Miller added: "We've got a big squad. There are a lot of players who have come in, so we have got strength in depth. I think all of us can complement each other."