Should I invest more in the same mutual fund if it’s NAV is falling?

While investing more when markets correct, may be a good thing, the actual strategy you take depends on a lot of factors:

1. Is the fund dropping faster than others? Is the fund doing better relatively to other funds?
2. What is your risk taking profile?
3. What is your current exposure to various asset classes (debt, equity etc)?
4. Is the market already very expensive or is it getting cheaper now.

Based on the above, you can take a call on investing more.