The simple and straightforward answer is NO. However, there are always instances where NIJ certification is not an option. However, HighCom would never recommend buying a Level III or IV armor insert or any Level II to IIIA soft armor products that are not NIJ compliant and on the NIJ Compliant Products List.
NIJ offers ballistic standards for other protective products such as shields, helmets, and protective gear outside of vests and plates. These standards do not have an official certification compliance program and are used for testing and evaluation benchmarks for the industry. In these cases you may run into helmets that are tested in accordance with NIJ 0106.01 or shields tested in accordance with NIJ 0108.01. As long as the supplier is able to provide legitimate testing results from a reputable laboratory you may want to then move onto your validation and performance testing internally of the product.
Steel is a unique material and typically AR500 or MILSPEC 46100 that is thick enough will provide some protection against handgun and in certain instances rifle threats depending on the processing and finishing of the steel itself. Steel is a cheap and versatile material for your everyday citizen to own for personal protection bu we woudl never recommend for law enforcement or military deployment purposes. Some Steel suppliers offer non certified plates that may be acceptable as long as they can provide proof of a series of lab results showing performance of protection.