It depends. If you have an active bass, probably not. If you have a passive bass, you might want to get an active DI because the line input of your mixer could be loading down your pickups, making them sound muddier than they should.
A DI box is really there to take your unbalanced, instrument level signal and turn it into a balanced, mic level signal to feed the mic preamp on your mixer or interface. It also isolates the bass from the mic preamp so you don't get any ground loops.
The reason the answer to your question isn't always clear is because there are too many variables. Some mixers have instrument inputs, which means you don't need a DI
Some basses have active circuitry which essentially puts out a line level signal, so you don't need a DI
But plugging a passive bass into a line level input will be really weak in both level and tone, a DI box will fix that.
Is there something you don't like about the sound you are getting? If not, just keep doing what you are doing.