With the exception of states with only one representative, this does not currently happen. As a general rule, it cannot happen unless Congress changes federal law. The Constitution grants Congress the power to make or modify regulations regarding the time, place, and manner of congressional elections, and Congress has done so. They have passed a law (2 USC 2c) requiring states to divide up their state into districts and elect one member per district.
There is, however, a possible way a state could get at-large representatives without another act of Congress. A different and older law (2 USC 2a) goes into more detail about redistricting, including what happens if states don't redistrict into a number of districts equal to the number of representatives:
- If the number stayed the same, the state keeps electing from the districts it was already using (and any at-large representatives stay at-large)
- If the number of representatives increased, all the new representatives are elected at large (and the old ones keep their districts or at-large status)
- If the number decreased, but there are still fewer districts than representatives, there's one representative per district and the remaining members are elected at-large
- If the number decreased and there are now fewer representatives than districts, then all representatives are elected at-large.