Johnson, the No. 16 overall pick in the 2015 draft, is expected to compete for a starting job opposite Bills top cornerback Tre'Davious White. That job was held late last season by undrafted rookie Levi Wallace after the midseason release of veteran Phillip Gaines and sudden early-season retirement of Vontae Davis.
Johnson, 26, was scheduled to be paid a base salary of $9.069 million in 2019 on the fifth-year option in his rookie contract with Houston. The terms of his deal with the Bills are not yet known.
He was placed on injured reserve last season after suffering a concussion in a Week 1 loss to the New England Patriots. It was his second concussion in less than a month, as he also left Houston's preseason game against the San Francisco 49ers on Aug. 19 after hitting his head on the field.
He told the Houston Chronicle that he has been medically cleared by neurologists to return.
"They told me I'm cleared, good to go and I'm in great shape moving forward," Johnson told the newspaper. "I'm feeling good. I'm going to be ready to go next season."
Johnson played in 35 games for the Texans, making 18 starts. He has one interception, 14 passes defensed and 122 tackles in four seasons.
ESPN's Sarah Barshop contributed to this report.