Because of its winter annual growth cycle, it is often easier to physically pull out once flowering begins. It does self-seed which of course is how it survives year-to-year and increases in population size. If it were in a situation where herbicides could be used, such as in grassy areas, conventional post-emergence broadleaf weed killers will provide control or, simply keep it mowed and prevent the formation of seed - the parent plant will eventually die off on its own due to its being a winter annual.
Treating the newly formed rosettes in the fall (which by the way may occasionally flower too) is also a good way to achieve control. When henbit is located in landscape beds, other desirable broadleaf plants in those same beds may be at risk for injury by post-emergence broadleaf herbicides used to control henbit. Therefore, a combination of hand removal plus careful spot treatment of individual henbit plants will help minimize herbicide injury risk to those desirable plants. Also, be sure to use herbicides formulated for low volatility, such as the amine forms, so that volatilization on a warm day following application won't result in off-target volatilization injury to desirable plants.