Your father has recently taken tb treatment and has been declared cured by a doctor so let`s presume that he is cured of tb for the time being. There can be many other causes for fever
. Does he have any other associated symptoms. If fever continues for some more time, he should consult his doctor and take a complete health check including relevant investigations. There are definitely chances of getting tb a second time or even reactivation of tb in the body. Fever may or may not be a symptom of cancer. That`s why i insist on a complete health check.