Are income from fixed maturity plan of MFs invested by NRIs taxable under DTC?

Yes, gains will be taxable @ 10% without indexation benefit (or 20% with indexation), if FMP is for more than a year. For less than a year FMP, gain will be added to Indian income and taxed as per slab rate.

Having said all this, this tax will only applicable if your income is above the taxable limit.