Johnson, who suffered a brain hemorrhage more than a month ago, has been working with parallel bars and participating in speech therapy, including naming objects, his office said in a statement.
That includes strengthening exercises to gain mobility on his right side, said Dr. Philip Marion, head of rehabilitation at George Washington University Hospital. Johnson's right side was weak when he arrived at the hospital Dec. 13.
His recovery is expected to take several months.
The Democratic senator from South Dakota was rushed to the hospital after becoming disoriented during a phone call with reporters and underwent emergency surgery hours later. He was diagnosed with arteriovenous malformation, a condition, often present from birth, that causes arteries and veins to grow abnormally large, become tangled and sometimes burst.
He was sedated and on a ventilator for several weeks due to fluid that developed in his lungs as a result of the initial hemorrhage. He was upgraded from critical to fair condition on Jan. 9 and has since been moved from intensive care to inpatient rehabilitation.
Johnson's sudden illness raised questions about the Democrats' one-vote majority in the Senate. South Dakota's Republican governor, Mike Rounds, would appoint a replacement if Johnson's seat were vacated by his death or resignation.
Johnson's wife, Barbara, said in a statement that her husband "develops more skills each day and typically exceeds the goals that others set for him."