I will be apply for a short term study visa but my fathers bank statement which I will be using doesn’t show any activity in the past 6 months other than a deposit of 3,000 USD which he got out of an investment. The balance is 21,000 . Is it fine if the bank account isn’t very active ?
Generally speaking, no. What they want to see is not simply a large amount of money, they want to see documented, legal income balanced against reasonable expenses, with income in excess of expenses.
Gayot Fow explains this at length in another answer. Your case would be his second example under "Funds Parking."